the fish

Identity

Biological features

Body elongated and cylindrical, round abdomen, compressed at the rear; standard length is 3.6-4.3 times of body height and 3.8-4.4 times of head length; length of caudal peduncle is larger than the width; head medium; terminal mouth and arch-shaped; upper jaw extends slightly over lower jaw, its rear can reach below eye; snout width is 1.8 times of the length, snout length is about the nasal distance; no palpus; gill rakes short and sparse (15-19); two rows of pharyngeal teeth on each side, laterally compressed, formula 2.5-4.2, inner row stronger, grooves on the lateral surface; scales large and cycloid; extreme 39-46 scales in lateral line, lateral line extends to caudal peduncle. Anus close to anal fin; Dorsal fin ray: 3,7; pectoral fin ray: 1,16; ventral fin ray: 1,8; anal fin ray: 3,8; caudal fin with around 24 rays; body color: greenish yellow laterally, dorsal portion dark brown; greyish white in abdomen.

Profile

Historical background

Grass carp culture began in the areas along the Yangtze and Pearl Rivers in the southern part of China. Compared to common carp, the culture of grass carp started much later. According to historical records, the culture of grass carp was closely related to the will of the current governor.

In the Tang Dynasty (618-904 A.D.), the family name of the emperor happened to be pronounced the same in Chinese as common carp, the only fish cultured then. The royal family prohibited common carp to be sold and killed by the people. Therefore, grass carp was chosen by the farmers as a substitute for aquaculture together with silver carp, bighead and black carp; this was because the seed of these fish were easily available in the areas along the Yangtze River and the Pearl River.

The culture of grass carp remained relatively small in scale due to the dependence on the natural supply of seed. Success in induced breeding technology significantly promoted its culture. The fish has been introduced to more than 40 other countries; sometimes it is referred to as the white amur.

About 10 000 tonnes/yr in 1950, the global production of farmed grass carp had reached over 100 000 tonnes/yr by 1972, exceeded 1 million tonnes/yr by 1990, and has been above 3 million tonnes/yr since 1999. China is by far the major producer (3 419 593 tonnes in 2002, 95.7 per cent of the global total).

Main producer countries

In 2006, many countries reported cultured production of grass carp to FAO but only some of them (Bangladesh, China, Taiwan Province of China, Islamic Republic of Iran, the Lao People's Democratic Republic, Myanmar and Russian Federation) reported a production greater than 1 000 tonnes.

Habitat and biology

Grass carp is a native Chinese freshwater fish with a broad distribution from the catchment area of the Pearl River in southern China to that of the Heilongjiang River in northern China. It has been introduced to about 40 other countries and there have been limited reports about the natural populations occurring in those areas; for instance, a natural population exists in the Red River in Vietnam.

It inhabits lakes, rivers and reservoirs. It is a basically herbivorous fish that naturally feeds on certain aquatic weeds. However, the fry/larvae feed on zooplankton. Under culture conditions, grass carp can well accept artificial feed such as the by-products from grain processing, vegetable oil extraction meals, and pelleted feeds, in addition to aquatic weeds and terrestrial grasses. Grass carp normally dwell in mid-lower layer of the water column. Comparatively, it prefers clear water and can move swiftly.

It is a semi-migratory fish; the mature broodstock migrate to the upper reaches of major rivers to propagate. Flowing water and changes in water level are essential environmental stimuli for natural spawning. The fish can reach sexual maturity under culture conditions, but cannot spawn naturally. Hormone injection and environmental stimuli, such as flowing water are necessary for induced spawning in tanks. Gras carp grow rapidly and reach a maximum weight of 35 kg in the wild.

Production

production systems

Various production systems are currently used for the culture of grass carp the major ones include semi-intensive and intensive culture ponds, and pens and cages in open waters.

Seed supplu

At present artificial propagation is the major supply of seed for the culture of grass carp, although natural seeds are still available in some rivers of China. Seed collected from the wild is mainly used for maintaining the genetic quality of the broodstock. Broodstocks used for artificial propagation are usually raised in captivity from seeds from the wild or from breeding stations where good natural stocks are maintained.

Hatchery production

Well-matured breeders are released into the spawning tank (round cement tank with diameter of 6-10 m and water depth of around 2 m) after being injected with inducing hormone (usually LRH-A). Water circulation is maintained throughout the spawning period.

Eggs are transferred to hatching raceways or jars, either manually or by gravity. Hatching raceways (which are round or ellipse-shaped structures) are commonly used for large-scale production. The width of the raceways is normally 0.8 m and the depth is 0.8-1.0 m. The inlets are mounted on the bottom of the raceways with openings in the same direction and at an angle of around 15° to the bottom, to promote water circulation. Screens are mounted on the inner wall for discharging water during the operation. Water can be totally drained out through the outlet on the bottom. Current flow is maintained during the hatching period to keep the eggs and larvae suspended in the water column.

In India, dry or wet stripping methods are used for the seed production of grass carp. Pituitary extract or synthetic agents such as ovaprim are used for induction (John Stephen Kumar, pers. comm. 2004).

Nursery

Earthen ponds (usually 0.1-0.2 ha and 1.5-2.0 m deep) are used for the nursing of grass carp. Ponds are chemically cleared, normally with quicklime, to eliminate all harmful organisms after totally drying. The usual dose is 900-1 125 kg/ha.

Organic fertiliser, animal manure and/or plant wastes (‘green manure‘) is commonly applied to increase the natural biomass of algae and zooplankton 5-10 days before the stocking, according to the water temperature. The quantity of organic fertiliser used is usually 3 000 kg/ha for animal manure or 4500 kg/ha for green manure. Green and animal manures can be used simultaneously but the quantity of each should be reduced accordingly.

Monoculture is practiced in the nursery stage, with a stocking density normally ranging between 1.2-1.5 million/ha, depending on the length of rearing and targeted size. The nursery operation usually takes 2-3 weeks in China.

Organic fertilisation is carried out at frequencies and rates sufficient to maintain high pond fertility and therefore a good supply of natural food organisms (especially zooplankton) for the fish. The quantity ranges from 1 500-3 000 kg/ha once every 4-5 days for animal manure or green manure, depending on existing water fertility.

Soybean milk can also be used as both direct feed and fertiliser to replace organic fertiliser in the nursery stage. The normal quantity is 3-5 kg (dry soybean)/100 000 fish daily. This usually means production costs are high. A paste-form of soybean cake or other by-products from grain processing is applied from the 5th day after stocking, usually at a rate of 1.5-2.5 kg/100 000 fish daily.

A paste of water peanut, water lettuce and water hyacinth can also be used to replace the above-mentioned feed and fertilisers at the rate of 25-40 kg/100 000 fish daily. 0.5 per cent of table salt needs to be added to the paste of water peanut to remove its saponin toxicity. Normal survival rates in nursery ponds are 70-80 per cent, although it may reach over 90 per cent under good management.

The fish usually reach the size of about 30 mm in length after 2-3 weeks of rearing. These are called summer-fingerlings in China and are ready for the fingerling rearing stage. Conditioning, through careful netting and holding the fish at high density for a while (several hours) is required before the transfer of summer-fingerlings to the fingerling pond. This practice is designed to fish tolerance to stress before they are transported.

Rearing fingerlings

Summer-fingerlings are not suitable for direct stocking in grow-out ponds; they need to be reared to the fingerling stage (13-15 cm in length or larger) first. The technique for fingerling rearing is rather different to the nursery operation, especially when grass carp are stocked as the major species. The major differences include the following:

• Relatively larger (0.2-0.3 ha) and deeper earthen ponds are used for fingerling rearing.
  
  
• Contrary to the nursery stage, polyculture is usually adopted for the production of grass carp fingerlings (monoculture at this stage is quite rare). Grass carp can be polycultured with other carp species except black carp (Mylopharyngodon piceus).
  
  
• The stocking density is 120 000-150 000/ha when it is the major species in the pond or 30 000/ha when it is the secondary species.
  
  
• Feeding is vitally important throughout the fingerling rearing period. Grass carp are mainly fed with Wolffia arrhiza when it is between 30-70 mm in length. The initial feeding rate is 10-15 kg/10 000 fish daily and is gradually increased according to the demand of the fish. The feed is changed to duckweed (Lemna minor) when the fish is between 70-100 mm in length. After that, the fish can be fed with tender aquatic weeds and terrestrial grasses. In addition, commercial feeds (soybean cake, rapeseed cake, wheat bran, rice bran, etc.) are also fed at a daily rate of 1.5-2.5 kg/10 000 fish.
  
  
• Fingerling rearing normally takes 4-6 months for above mentioned size and stocking density in China. The period can be considerably shortened in warmer climates or if lower stocking densities are used.
  
  
• The normal survival rate through the whole fingerling rearing period should be above 95 per cent.

It is difficult to culture grass carp from the yearling size (13-15 cm) to marketable size (>1 500 g) within one year in most parts of China; it is therefore common practice to rear yearlings to 2 year old fingerlings for grow-out stocking. The stocking density is much reduced, compared to the rearing of yearlings. The feeding regime is similar but the rate is much higher. By the end of this period, the fish have usually reached about 250 g. This practice is not necessary in tropical and subtropical areas, where yearlings of grass carp can reach marketable size within one year, due to high temperatures.

In Vietnam, the rearing of grass carp before the grow-out stage is divided into two periods. Fry are first raised to 4-5 cm, with a stocking density in the earthen nursery pond of 200-250 fry/m². The rearing period is normally 1.5-2 months. Then the fish are further raised for about 2 months to a size of 12-15 cm at a much lower density. The fish is mainly fed with soybean powder, rice bran, maize powder and aquatic plants (Azolla sp.) after reaching 3 cm in body length.

The nursery rearing of grass carp in India is carried out in intensively fertilised ponds, adequately enriched with zooplankton and unicellular algae. Generally the survival of fry is about 70-80 per cent in well-managed nursery ponds. In addition to the natural feeds developed, supplementary feeding with powdered groundnut oilcake and rice polishings or bran is also practiced (John Stephen Kumar, pers. comm. 2004).

Ongrowing techniques

The most commonly adopted ongrowing techniques for grass carp include polyculture in ponds and pen and cage culture in lakes and reservoirs.

Semi-intensive to intensive polyculture in ponds in China

For polyculture in ponds or pens, grass carp can be stocked either as the major species or a secondary species together with other carp species. The total stocking density is 750-3 000 fish/ha with a stocking size of 125-250 g. Aquatic weeds and terrestrial grasses form the major feed for grass carp in grow-out culture. Feeding commercial feeds such as pellets and by-products from vegetable oil extraction and grain processing are becoming more popular as a means of replacing aquatic weeds and grasses to save labour costs in pond culture. The yield of grass carp is usually 1 000-3 000 kg/ha, which accounts for 15-40 per cent of the total production.

Intensive culture in cages in China

In intensive culture systems in cages, grass carp are usually stocked as major species. Cages are usually about 60 m², with a depth of 2-2.5 m. 250-500 g fish are stocked at 10-20/m³, depending on the targeted production. In addition, 30-50/m³ Wuchang fish (bluntnose black bream, Megalobrama amblycephala), are also stocked at a size of 80-125 g. Silver and bighead carp are also stocked at 1 per cent of the total, as 'cage cleaners'.

The fish are fed with aquatic weeds/terrestrial grasses and pelleted or other commercial feeds. The culture period is usually 8-10 months and the yield is normally 30-50 kg/m³. Grass carp usually account for 60-70 per cent of the total production. Cage culture of grass carp through the use of commercial feeds involves relatively high production costs.

Feeding efficiency is not always as high in cage culture as in pond culture so, where terrestrial grass and aquatic weeds are locally abundant, collecting them and applying them in cage culture usually requires less labour input as the transportation is limited.

Grow-out systems in other countries

The grow-out of grass carp is mainly conducted in earthen ponds and cages in Vietnam. Polyculture with other species (e.g. silver carp, common carp, rohu and mrigal etc.) is common. Grass carp may be stocked as either major or secondary species. Grass carp usually account for 60 per cent of the total stocking density of 1.5-3 fish/m² (dependent on the level of intensity) in ponds and the fingerling size is 5-6 cm (mountainous areas) and 12-15 cm (lowlands).

The stocking rate in cage culture is 20-30 fish/m³ but much larger fingerlings are used (normally 50-100 g). Grass carp are usually fed with terrestrial grasses, cassava leaves, banana stems and maize leaves in grow-out culture. Grass carp production usually accounts for 60 per cent of total production (7-10 tonnes/ha) in ponds. The marketing size for grass carp is 1-1.5 kg and 1.5-2.5 kg in ponds and cages respectively.

In India, grass carp are cultured as an important species in pond-based composite systems consisting mainly of Indian major carps and Chinese carps. The grass carp stocking density depends mainly on the availability of aquatic weeds and terrestrial grasses but is usually 5-20 per cent of the total. Aquatic weeds (Hydrilla, Vallisneria, Wolffia) and terrestrial grasses such as Napier grass and other hybrid grasses are the major feeds in grass carp farming. Normally, grass carp reach 0.5-1.5 kg in 8-10 months (John Stephen Kumar, pers. comm. 2004). The total production from such systems can reach 8-10 tonnes/ha/yr.

Feed supply

Grass carp can be reared with commercial feeds or natural food, such as aquatic weeds and grasses. They prefer relatively low fertility. Production is mainly limited by water quality. The commercial feeds used for grass carp are relatively low in protein (28-30 per cent) and their raw materials include soybean cake/dregs, rapeseed cake and wheat bran etc. Aquatic weeds can be collected from natural water bodies. Terrestrial grasses can be grown on the pond dyke with organic manure.

Harvesting techniques

Both selective and total harvesting are practiced for grass carp. Selective harvesting is usually conducted in the early morning (because temperatures are relatively low and for morning sales) during late summer and autumn. Individuals of marketable size are selected after netting (a single netting for each harvest). Total harvesting is carried out at the end of the culture period. Several nettings are usually carried out before total drain-down of the pond. All the fish are harvested at the end of the year, either for marketing or for restocking (individuals below marketable size) for the next production cycle.

Handling and processing

Grass carp is normally sold live or fresh. A small quantity of the production is processed by ready-to-eat food stores; in this case the most commonly used processing method is deep frying.

Production costs

The production cost of grass carp vary according to the culture practice used but are normally about USD 0.50/kg of fish produced. Feed costs comprise the largest portion of production costs.

Diseases and control measures

Farmed grass carp are rather susceptible to various diseases. Major diseases and methods of control are listed in the table below.

However few, if any, cultural environments are ideal. Constant fluctuations in the environment and the interaction of genetic limitations and viral ecology assure that diseases will be an ever present problem in monoculture rearing environments.

Principles of minimizing the impact of diseases on animal populations are well established in other areas of aquaculture and agriculture. With each year we become able to detect even smaller levels of potential pathogens quicker, causing continual shifts in issues concerning carrier status and minimizing the stress on populations.

What is White Spot?

The term white spot is a description of the characteristic white spot appearance that has accompanied outbreaks of this viral disease around the globe.

• The mere appearance of white spots is not necessarily indicative of the disease that is caused by this virus. Other things can cause white spots.
  
  

• In P. vannamei, though there are white spots, in the disease in the field, they appear late in the infectious cycle and are much smaller than the classic spots noticed in other shrimp species. Classic spots from P. monodon are shown below.

The disease due to the WSSV in P. vannamei is not consistent in its impact. Some areas have been dramatically impacted with total crop failures while others seem to be living with the virus without acute mortality. Only time will tell if this is a permanent pattern. Thailand apparently experienced a similar situation before the problem increased dramatically. It is likely that as the virus spreads and becomes more firmly entrenched in the farm environments that more frequent and severe outbreaks will occur.

What causes the problem?

The disease is associated with a group of viruses that appear to be similar in genetic composition and are widely dispersed geographically. There is some evidence that suggests that not all of the variants are identical though this is the subject of ongoing research. The virus is very large, as viruses go, and has an envelope around it. It is very susceptible to iodine and chloroform and the transmission cycle appears to be easily broken.

Viruses require the host’s metabolic machinery to reproduce themselves and can not be eradicated with antibiotics. However, antibiotics can impact secondary bacterial infections and in theory might be useful if a bacterial infection is stressing animals leading to increased susceptibility.

What is PCR?

PCR is an acronym for Polymerase Chain Reaction. This technique is a valuable tool that enables the detection of minute quantities of DNA. Almost all organisms contain DNA as the primary genetic material, including viruses though some contain RNA. Using a piece of DNA that reacts with the viral DNA it is possible to “fish” for the presence of the virus DNA in a sample. When this piece of DNA reacts with the viral DNA the amount of this reactive DNA is amplified many times over, a billion fold or more. This makes PCR a very sensitive method for detected the DNA of any particular pathogen of interest. While PCR is just coming in to its own as a potential health management tool, it does however have some drawbacks.

• It is technically exacting and prone to occasional errors. False positives (reactions that suggest that you have the virus when you do not) can cause serious problems in that animals that are not carrying the virus can be labeled as carrying it. False negatives are even worse as this can result in keeping stocks that should not be kept.
  
  

• PCR tests need to be validated, sensitive, accurate and reproducible. Not all of the commercially available kits have been this thoroughly tested.
  
  

• PCR does not distinguish between the DNA of a live or a dead virus.
  
  

• PCR is not a quantitative technique. It does not tell you how much viral material there was to start with though it can be interpreted semi-quantitatively.
  
  

• PCR depends upon the sequence of the primers (small pieces of DNA) to react only with the organisms DNA that they have been constructed against. This high degree of specificity is a strength of the assay. Though the primer will react with isolates that are not as virulent as are others or are avirulent.
  
  

• When one is told that a population has been screened (say 150 animals out of a million) by PCR and all have come back negative, this does not mean that none of the animals in the population are carrying the virus. No technique is 100% unless every animal is screened and the technique is 100% accurate.

When sampling animals for the presence of a given pathogen, a specific number of animals are selected at random from the population for further examination. These numbers are based on well establish guidelines in fish health monitoring and certification. Supposedly at 150 out of 1,000,000 animals, you have a 98% chance of finding something that is there. Even if this were true, in a population of one million animals, you could still have 20,000 animals that were carriers. Since random sampling is not usually the case and the analytical techniques are not 100% effective at detecting the pathogen of interest this number could actually be much higher.

Do not rely on PCR as your only tool for protecting yourself against the virus. Like all other management tools it is just that and must be used in conjunction with other techniques to maximize its potential. Selecting larval suppliers that have a history of remaining free of the problem is one very useful tool as are others.

What can you do to lessen the impact of this disease on your farms and hatcheries?

There are some things that you can control and others that you can not.

What management techniques are going to be useful?

Do not buy nauplii or PL’s from a source that could be or is infected with the virus. It is likely that iodine and water washes remove and destroy the virus when used on eggs, nauplii and PLs. It is essential that this process be consistent. Hatcheries must maintain good biosecurity measures and examine each batch of animal. The hatchery needs to be constructed to prevent the introduction of the virus from the ocean.

Use the most sensitive and reliable diagnostic tests available to detect and monitor WSSV. These are going to be DNA based technologies such as PCR and in-situ-hybridization (ISH) of tissue lesions.

Sample hatcheries at least twice during the production cycle and retain samples for later testing (three weeks post shipping).

Only buy PCR screened and stress tested animals. Starting out with no or a very low virus load is important.

Stressing PL’s with formalin has been found to weed out weaker animals though one should never stock PLs that are known to be carrying the virus. It has been noted that in P. japonicus, the virus may not display its pathogenicity till after PL6, making the screening of later stage animals essential.

Minimize the stress on the shrimp wherever possible

There are some ways that you can do this and many that you can not. Some of the things that you can do are:

• increase acclimation times before stocking
  
  

• use non-specific immune stimulants (NSIS) and fortified mineral and vitamin diets to increase stress tolerance
  
  

• Consider stocking during times of the year that you know there will not be experiencing severe stresses from sudden changes in temperature and salinity. It has been reported that these types of stresses can precipitate an epizootic in a population that carries the virus.
  
  

• use good quality diets and continue the use of NSIS through out the life cycle
  
  

• stock at lower densities
  
  

• Monitor for the presence of vectors carrying WSSV in the ponds and control them.

Sample the phyto and zooplankton in the pond before stocking and test by PCR for WSSV. Positive ponds should be avoided.

Sample your ponds frequently. Assure that sick and dying animals and any unusual patterns of mortality are sampled as a routine by PCR and/or histopathology. At the first sign of a problem, harvest the shrimp if you can.

What are some of the ways that other countries manage this disease?

It is believed that one of the major methods for the movement of this virus (and others) has been the movement of infected PL’s. If this can be stopped, it should lessen the rate of spread of the virus. Many countries have taken steps to ensure this though how successful they will be will only be apparent with time. Once the virus gains a foothold it appears that it is there to stay. Fortunately as with all of the other viral diseases such as BP, IHHN, TSV, and MBV, the impact of the disease will lessen with time.

The Thai’s use a variety of tools to deal with the virus, some of which will be useful for P. vannamei. It is important to recognize the differences between the two forms of shrimp culture and understand that there are some difficulties associated with using the same tools to try and control the presence of the virus.

One recommendation made to and by Thai farmers is to use pesticides to kill the vectors before stocking the ponds. Usually a very potent pesticide is added to the water to kill any crustaceans and other vectors that might be present in the pond carrying the virus. This can not be done on the scale that would be required in most of the Americas. The costs would be quite high and the huge amounts of pesticides that would have to be dumped into the ecosystem are not desirable. This should be discouraged and only considered as a very last resort.

Filtering intake water into the pond is one viable approach to eliminating some vectors. Conventional filters may be problematic in the Americas due to the large demands for water. Though this demand can be moderated and relatively small amounts of water added to the system. Filters that use plant fibers to trap everything in conjunction with serial mesh filtration might be useful. Using 250 micron or smaller mesh filters including small mesh bags can be helpful as well.

Another recommendation is to avoid the exchange of water. There appears to be some merit in this in that recent outbreaks of WSSV in S. Carolina in the USA have been associated with the addition of water to ponds. Whether this stressed the shrimp and set off an epizootic or introduced vectors and virus into the ponds is not known. In intensive systems, aeration is used while it is not in semi-intensive systems. The ability to aerate the water mechanically without resorting water exchange might be very useful in those ponds where oxygen levels can not be managed without water exchange.

Animals that are positive for the virus by PCR are not purchased. In some cases it has been reported that screening stocked animals for the presence of the virus has been found to be a useful tool to follow the status of the disease in the population. This can be used to time harvests and to minimize the potential spread of problems to other ponds and/or neighbors.

What you can not control.

Probably the biggest single problem faced by shrimp farmers aside from the actions of their associates will be the sudden environmental fluctuations that accompany the rainy season. Sudden changes in salinity and temperature have been implicated in many outbreaks. As the disease moves from one area to another the viral load in the environment will increase to the point where the virus will be ever present. Ideally shrimp should be destroyed once they are ill to prevent high loads of the virus from entering the environment. Unfortunately this is usually not practical. Harvesting shrimp is and should be encouraged even if shrimp are too small to sell. Cutting losses and minimizing the spread of the virus are to the farmers advantage.

Use Immune Stimulants and optimize Nutrition

All of the data to date suggests that shrimp have relatively primitive immune systems that can not respond to vaccination. In fact it appears that you can not vaccinate shrimp in any sense of the word. Their immune response is short lived, non-specific in nature and provides a modest level of immunity. Though it is possible to exploit this with a variety of polysaccharides, there are very few reports of success using these compounds in the field. The compound with the most field data is a bacterial based material. Lab and field studies have shown a wide range of potential benefits, though like all other tools, these require that they be used as part of on overall management strategy geared towards minimizing the impact of the pathogen.

Animals that have lower levels of resistance due to inadequate nutrition are more susceptible to a variety of problems. Since shrimp in semi-intensive culture environments get between 50 and 70% of their nutrients from natural food source, it is usually difficult to assess what nutrients might be limiting. The role of vitamins A, B, C, D, and E and micro-nutrients such as Selenium are well documented in minimizing the effects of stress and should be routinely added to diets at higher than usual levels at times of stress.

Conclusions:

This virus disease is just one of the many that shrimp farmers will face in the years to come. Effective tools and techniques exist to determine how serious of a problem it can be and to moderate its impact at this time. We are fortunate to have the experiences of others to draw on. The use of PCR in conjunction with other management tools can affect how this disease impacts your bottom line.

Source: Aqua-In-Tech - Reproduced August 2005

Production

Production System

Seed supply

Captured wild seeds were used in Latin America for extensive pond culture of Penaeus vannamei until the late 1990s. Domestication and genetic selection programmes then provided more consistent supplies of high quality, disease free and/or resistant PL, which were cultured in hatcheries. Some were shipped to Hawaii in 1989, resulting in the production of SPF and SPR lines, leading to the industry in the United States of America and Asia.

Broodstock maturation, spawning and hatching

There are three sources for broodstock P. vannamei:

• Where they occur naturally, broodstock are sea-caught (usually at 1 year of age and weighing >40 g) and spawned.
• Cultured shrimp harvested from ponds (after 4–5 months at 15–25 g), are on-grown for 2–3 months and then transferred to maturation facilities at >7 months of age when they weigh 30–35 g.
• Purchased from tank-reared SPF/SPR broodstock from the United States of America, (at 7–8 months of age and weighing 30–40 g).

Broodstock are stocked in maturation tanks in dark rooms supplied with clean, filtered seawater. Feeds consist of a mixture of fresh and formulated broodstock feeds. One eyestalk from each female is ablated, leading to repeated maturation and spawning. Females of 8–10 months of age reproduce effectively, whilst males peak at >10 months. Spawning rates of 5–15 percent/night are achieved, depending upon broodstock source. Females are either spawned in communal or individual tanks (to avoid disease transmission). The following afternoon, the healthy nauplii are attracted by light, collected and rinsed with seawater. They are then disinfected with iodine and/or formalin, rinsed again, counted and transferred to holding tanks or directly to larval rearing tanks.

Hatchery production

Hatchery systems range from specialized, small, unsophisticated, often inland, backyard hatcheries to large, sophisticated and environmentally controlled installations, together with maturation units. Nauplii are stocked into flat, or preferably 'V' or 'U' shaped tanks with a volume of 4–100 m³, made from concrete, fibreglass or other plastic lined material. The larvae are either cultured to PL10–12 in a single larval rearing tank, or harvested at PL4–5 and transferred to flat-bottomed raceways/tanks and reared to PL10–30. Survival rates to PL10–12 should average >60 percent. Water is exchanged regularly (at 10–100 percent daily) to maintain good environmental conditions. Feeding normally consists of live food (microalgae and Artemia), supplemented by micro-encapsulated, liquid or dry formulated diets. From hatching, it takes about 21 days to reach harvest at PL12. Care is taken to reduce bacterial/pathogen contamination of the larval facilities using a combination of periodic dry-outs and disinfections, inlet water settlement, filtration and/or chlorination, disinfection of nauplii, water exchange and the use of antibiotics or (preferably) probiotics.

Nursery

Most farming operations for P. vannamei do not use nurseries, but transport PL10–12 at reduced temperature either in plastic bags or oxygenated transportation tanks to the pond and introduce them directly. In some instances, nursery systems are used and comprise separate concrete nursery tanks or earth ponds, or even net pens or cages located within production ponds. Such nursery systems may be used for 1–5 weeks. Nurseries are useful in colder areas with limited growing seasons, where PL are nursed to a larger size (0.2–0.5 g) in heated tanks/ponds, before stocking into ponds. The use of super-intensive, temperature-controlled, greenhouse-enclosed, concrete or lined raceways have given good results in the United States of America.

Ongrowing techniques

Ongrowing techniques can be sub-divided into four main categories: extensive, semi-intensive, intensive and super-intensive, which represent low, medium, high and extremely high stocking densities respectively.

Extensive

Commonly found in Latin American countries, extensive grow-out of P. vannamei is conducted in tidal areas where minimal or no water pumping or aeration is provided. Ponds are of irregular shape, usually 5–10 ha (up to 30 ha) and 0.7–1.2 m deep. Originally, wild seeds entering the pond tidally through the gate, or purchased from collectors were used; since the 1980s hatchery reared PL are stocked at 4–10/m². Shrimp feed mainly on natural foods enhanced by fertilization, and once-daily feeding with low protein formulated diets. Despite low stocking densities, small shrimp of 11–12 g are harvested in 4–5 months. The yield in these extensive systems, is 150–500 kg/ha/crop, with 1–2 crops per year.

Semi-intensive

Semi-intensive ponds (1–5 ha) are stocked with hatchery-produced seeds at 10–30 PL/m²; such systems are common in Latin America. Regular water exchange is by pumping, pond depth is 1.0–1.2 m and aeration is at best minimal. The shrimp feed on natural foods enhanced by pond fertilization, supplemented by formulated diets 2–3 times daily. Production yields in semi-intensive ponds range from 500–2 000 kg/ha/crop, with 2 crops per year.

Intensive

Intensive farms are commonly located in non-tidal areas where ponds can be completely drained, dried and prepared before each stocking, and are increasingly being located far from the sea in cheaper, low salinity areas. This culture system is common in Asia and in some Latin American farms that are trying to increase productivity. Ponds are often earthen, but liners are also used to reduce erosion and enhance water quality. Ponds are generally small (0.1–1.0 ha) and square or round. Water depth is usually >1.5 m. Stocking densities range from 60–300 PL/m². Heavy aeration at 1 HP/400–600 kg of harvested shrimp is necessary for water circulation and oxygenation. Feeding with artificial diets is carried out 4–5 times per day. FCRs are 1.4–1.8:1.

Since the outbreak of viral syndromes, the use of domesticated disease free (SPF) and resistant (SPR) stocks, implementation of biosecurity measures and reduced water exchange systems have become commonplace. However, feed, water exchange/quality, aeration and phytoplankton blooms require carefully monitoring and management. Production yields of 7–20 000 kg/ha/crop, with 2–3 crops per year can be achieved, up to a maximum of 30–35 000 kg/ha/crop.

In the 'bacterial floc' system, the ponds (0.07–1.6 ha) are managed as highly aerated, recirculating, heterotrophic bacterial systems. Low protein feeds are fed 2–5 times per day, in an effort to increase the C:N ratio to >10:1 and divert added nutrients though bacterial rather than algal pathways. Stocking at 80–160 PL/m², the ponds become heterotrophic and flocs of bacteria are formed, which are consumed by the shrimp, reducing dependence on high protein feeds and FCR and increasing cost efficiency. Such systems have realized productions of 8–50 000 kg/ha/crop in Belize and Indonesia.

Super-intensive

Recent research conducted in the United States of America has focused on growing P. vannamei in super-intensive raceway systems enclosed in greenhouses, using no water exchange (only the replacement of evaporation losses) or discharge, stocked with SPF PL. They are thus biosecure, eco-friendly, have a small ecological footprint and can produce cost-efficient, high quality shrimp. Stocking 282 m² raceways with 300–450 0.5–2 g juveniles/m² and ongrowing for 3–5 months has realized production of 28 000–68 000 kg/ha/crop at growth rates of 1.5 g/week, survivals of 55–91 percent, mean weight of 16–26 g and FCRs of 1.5–2.6:1.

Feed supply

P. vannamei are very efficient at utilizing the natural productivity of shrimp ponds, even under intensive culture conditions. Additionally, feed costs are generally less for P. vannamei than the more carnivorous P. monodon, due to their lower requirement for protein (18–35 percent compared to 36–42 percent), especially where bacterial floc systems are used. Feed prices for P. vannamei range from USD 0.6/kg in Latin America and Thailand to USD 0.7–1.1/kg elsewhere around Asia; FCRs of 1.2–1.8:1 are generally obtained.

Harvesting techniques

Extensive and semi-intensive ponds are harvested by draining the pond at low tide through a bag net installed in the outlet sluice gate. If the tide does not allow harvesting, the water can be pumped out. In some larger farms, harvesting machines pump shrimp and water up to the pond bank where they are dewatered. Intensive ponds may be harvested similarly and small 2–6 man seine nets are dragged around the pond to corral shrimp to the side of the pond from where they are removed by cast or dip net or perforated buckets.

Partial harvesting is common in Asian intensive culture after the first 3 months. In Thailand, artificial sluice gates are temporarily installed inside one corner of the pond to harvest closed system ponds. Shrimp are then trapped in nets attached to this temporary gate when the pond is pumped out.

In super-intensive systems, the shrimp are simply harvested with large scoop nets when required for processing.

Handling and processing

If shrimp are sold directly to processing plants, specialized teams for harvesting and handling are commonly used to maintain shrimp quality. After sorting, shrimp are washed, weighed and immediately killed in iced water at 0–4 °C. Often sodium metabisulphate is added to the chilled water to prevent melanosis and red-head. Shrimp are then kept in ice in insulated containers and transported by truck either to processing plants or domestic shrimp markets. In processing plants, shrimp are placed in iced bins and cleaned and sorted according to standard export sizes. Shrimp are processed, quickly frozen at -10 °C and stored at -20 °C for export by ship or air cargo. Due to an increasing demand, no taxes and higher profit margins, many processing plants operate value-added product lines.

Production costs

Production costs vary depending on many factors. Operational costs for seed production averages USD 0.5–1.0/1 000 PL, whilst sales prices vary from USD 0.4/1 000 PL8–10 in China and USD 1.0–1.2/1 000 PL12 in Ecuador to USD 1.5 3.0/1 000 PL12 around Asia. Lower feed costs and higher intensity levels result in mean production costs for ongrowing of approximately USD 2.5–3.0/kg for P. vannamei, compared to USD 3.0–4.0/kg for more extensive P. monodon culture.

by Ruth Francis-Floyd, Craig Watson, Denise Petty, and Deborah B. Pouder, University of Florida IFAS Extension.
from http://www.thefishsite.com/

Introduction

Ammonia causes stress and damages gills and other tissues, even in small amounts. Fish exposed to low levels of ammonia over time are more susceptible to bacterial infections, have poor growth, and will not tolerate routine handling as well as they otherwise would. Ammonia is a killer when present in higher concentrations, and many unexplained production losses have likely been caused by ammonia.

Ammonia accumulates easily in aquatic systems because it is a natural byproduct of fish metabolism. All animals excrete some waste in the process of metabolizing food into the energy, nutrients, and proteins they use for survival and growth. In fish, the principal metabolic waste product is ammonia. Because it is continuously excreted and potentially lethal, successful aquaculture operations must therefore incorporate methods to detect and eliminate ammonia before it can accumulate and harm fish.

A byproduct of protein metabolism, ammonia is primarily excreted across the gill membranes, with only a small amount excreted in the urine. The decay of uneaten feed and organic matter create small amounts of ammonia, but in most aquaculture systems, fish themselves are the primary source of the compound. The more feed a fish receives, the more ammonia it will produce. However, even a starved fish will produce some ammonia.

Ammonia may be present in city or well water. Even trace amounts can be toxic to fish, and ammonia is colorless, and, in small amounts, odorless. Therefore, the only way for an aquarist or producer to know if ammonia is present is to test the water.

In water, ammonia occurs in two forms, which together are called total ammonia nitrogen, or TAN. Chemically, these two forms are represented as NH₄+ and NH₃. NH₄+ is called ionized ammonia because it has a positive electrical charge, and NH₃ is called un-ionized ammonia (UIA) because it has no charge. This difference is important to know because NH₃, un-ionized ammonia, is the form more toxic to fish. Both water temperature and pH affect which form of ammonia is predominant at any given time in an aquatic system.

The Nitrogen Cycle

A biological process called the nitrogen cycle eliminates ammonia from the water by converting it to other, less toxic compounds (Figure 1). The ammonia fish excrete is converted to a compound called nitrite (NO₂-) by several genera of bacteria, including Nitrosospira and Nitrosomonas. Other groups of bacteria, including Nitrospira and Nitrobacter, convert nitrite to nitrate (NO₃-).

In ponds, this process takes place in the surface layers of the mud, and on plants or other structures. In tanks or aquaria, a biological filter, or biofilter, must be provided as a place where the bacteria can live and flourish. A new biofilter requires six to eight weeks to build up sufficient bacteria to effectively reduce ammonia and nitrite levels.

Other important points to mention about the nitrogen cycle are that both groups of nitrifying bacteria need oxygen and alkalinity to function. If oxygen levels are not sufficient, the process can break down, and ammonia and nitrite levels will increase. Alkalinity (bicarbonate and carbonate) is also used by the nitrifying bacteria. If alkalinity is less than 20 mg/L, the nitrifying bacteria will not be able to function.

It's also important to note that nitrite is toxic to fish at levels as low as 0.10 mg/L. If the biofilter is immature or impaired, adding chloride in the form of salt (sodium chloride) or calcium chloride at the rate of 10 mg/L chloride for each 1 mg/L nitrite will reduce the toxic effects of nitrite on fish.

Nitrate, the end product of the nitrogen cycle, is considered to be harmless to fish in natural systems and ponds as it is used as a fertilizer by plants, including phytoplankton. In closed systems with little or no water exchange, however, nitrate will accumulate and may be harmful if higher than 250 mg/L.

Ammonia Testing

All aquaculturists and hobbyists should invest in a water quality test kit. A good water quality management program will reduce fish disease problems, promote growth, and lessen the need for chemical treatments. A water quality test kit will pay for itself many times over, both in numbers of fish saved and increased production.

Most commercial ammonia test kits measure the total ammonia nitrogen (TAN). Again, it is the un-ionized ammonia (or UIA) portion of the TAN that is more toxic. The UIA fraction of the total TAN can be determined from the TAN measurement if you know the temperature and pH of the water. At high temperatures and high pH, there is more UIA. Therefore, a good ammonia test kit will include a TAN test, a pH test, and a thermometer.

There are two types of ammonia test kits, and each uses a different testing method to determine TAN. One is the Nessler's method and the other is the ammonia salicylate method. If formalin or formalin-containing products have been used within 24-72 hours to treat fish for parasites, the Nessler's method will result in a falsely elevated ammonia reading. Use of ammonia binding products will also cause false high ammonia readings with the Nessler's method. The reagent used in the Nessler's method contains a small amount of mercury that in many states must be disposed of as hazardous waste.

The other testing method is the ammonia salicylate method. This method is not affected by ammonia binding products or formalin treatments. The ammonia salicylate method is also more accurate than the Nessler's method when testing ammonia in seawater, and it does not require disposal of a hazardous waste.

When Should Ammonia Be Tested?

If stocking densities are high, ammonia should be tested every 10 to 14 days in ponds, and at least once a week in tanks. If multiple tanks depend upon a common biofilter (i.e., a recirculating system), there is no need to check every tank individually. Keep records for all tests, and whenever ammonia is found, increase the frequency of testing until the problem is corrected. Whenever fish are sick, test the water quality.

Ammonia is responsible for more unexplained losses in aquaculture than any other water quality parameter. As previously mentioned, it is colorless and odorless, so the only way to know if it is present is to test for it. Fish submitted to a diagnostic laboratory are tested for diseases (bacteria, parasites, fungi or viruses) only. It is the responsibility of aquarists and producers to test the water quality, which is very likely to be the underlying problem.

Interpreting the Ammonia Test

In healthy ponds and tanks, ammonia levels should always be zero. Presence of ammonia is an indication that the system is out of balance. Therefore, any ammonia in a pond or tank should alert the producer to start corrective measures. Un-ionized ammonia (UIA) is about 100 times more toxic to fish than ionized ammonia.

This UIA toxicity begins as low as 0.05 mg/L, so the result of the TAN test needs to be further calculated to find the actual concentration of UIA. To do this calculation, the temperature and pH need to be measured. Once the pH and temperature are known, the fraction of UIA can be calculated using a multiplication factor found in Table 1. Find the temperature on the top row of the table, and the pH in the left column. The number at which the appropriate column and row intersect in the table is multiplied by the TAN to give the UIA in mg/L (ppm).

This calculation is summarized in Figure 2 and an example is given in Figure 3. Anytime the UIA is higher than 0.05 mg/L, the fish are being damaged. As the concentration rises above 0.05 mg/L, it causes more and more damage. At 2.0 mg/L, the fish will die. Again, any ammonia indicates a problem in your system. If you find it, take corrective measures immediately.

Management of an Ammonia Problem

The first thing to do when ammonia is present in a pond or tank is to reduce or eliminate feeding. Fish are not likely to eat during periods of ammonia stress and the uneaten feed will only make the situation worse. Overfeeding is a major cause of high ammonia concentrations, and stopping the feeding will allow the natural nitrogen cycle to "catch up" with the nutrient load. If at all possible, a 25 per cent to 50 per cent water change will help to remove some of the ammonia. This is only feasible in small ponds or tanks, so don't try to solve an ammonia problem in a large pond by this method.

Low levels of dissolved oxygen limit the ability of nitrifying bacteria to convert ammonia and nitrite, so it is important to monitor dissolved oxygen.

In ponds, the addition of a phosphate fertilizer may help to relieve high TAN levels over a period of days by stimulating phytoplankton growth, which helps remove ammonia from the system; however, it may not help quickly enough in an acute ammonia crisis. Use a 0–20–0 fertilizer at a rate of 40 pounds per acre. It is important not to use a fertilizer that contains nitrogen because nitrogen will add to the problem. If phosphorus is not a limiting factor for algal growth in the pond, the phosphate fertilizer method will not work at all.

In tanks without a biofilter, the producer or aquarist should consider incorporating one. Given the six to eight weeks necessary to establish a biofilter, this will not help in a crisis, but it is a long-term solution to the problem.

In the short term, water changes and the use of ammonia binding products will alleviate ammonia toxicity. It's important to remember that these are short-term solutions. For long-term management, it's best to establish a biofilter.

Some chemicals used to treat diseases in fish, especially antibiotics, can be detrimental to the nitrifying bacteria in the biofilter. Both ammonia and nitrite levels should be tested more frequently after applying a disease treatment, to ensure that the biofilter is still functioning.

Summary

Ammonia is a major waste product of fish and the breakdown of feed and other organics. It can accumulate in aquaculture or aquarium systems, where it will, at the very least, decrease production. It is frequently a stressor that leads to disease, and in other cases it kills fish directly. The only way to detect its presence is to test for it. A fish farmer or aquarist should invest in a water quality test kit, learn how it works, and use it regularly.

Ammonia test kits only measure the total ammonia nitrogen (TAN). When this test indicates a reading above zero, producers or aquarists can determine the fraction of toxic un-ionized ammonia (UIA) after measuring pH and temperature. The multiplication factors are found in Table 1, and an example calculation is found in Figure 3.

When ammonia is present, the fish in the system should not be fed until the problem is corrected. In small systems, a water change will help, and in large ponds, a 0–20–0 fertilizer may help.

Test for ammonia regularly and take corrective measures as soon as you detect it. Severe problems may occur when tests are not performed frequently enough. Once fish have started to die, it is difficult to correct an ammonia problem without losing more fish.

However, as price control is exercised carefully to avoid consumer backlash, the catering and retail trade have moved to make cheaper products available to end consumers.

Subsequently, demand for large sizes shrimp did not improve much during the Golden Week festival compared to the previous years. The festival demand for X–large sizes namely 6/8 through 13/15 was disappointing for the catering trade.

Imports during the first quarter of the year fell behind last year’s. Shrimp prices at wholesale trading; however, were stable during this period following reduced imports during the first quarter of the year.

MARKET TRENDS

The H1N1 flu (known as Mexican flu in Japan) alarm has created mixed trends in the market. Due to the health scare, people are avoiding going out, which is hurting the already soft restaurant trade. Supermarkets, on the other hand, report increasing sales of frozen food including processed and prepared shrimp as more meals are prepared or eaten at home. Usage of cooked and peeled shrimp has increased at pizza outlets.

Due to the shrinking business in the catering trade, imports of sushi shrimp will be lower this year. Less traveling during this summer holiday will also take a toll on the already affected catering trade.

In a seasonally dull market in hot and humid summer, trading is sporadic for small lots and selective sizes at wholesale/distribution level. Prices have weakened further for 16/20 counts b/tiger shrimp, for which demand is extremely poor and local stocks are high. This downward price movement also affected prices for the mid- range counts (21/25 and below). Supply shortage from Kolkata area may reverse the situation. Supermarket demand for frozen vannamei is better; prices are under pressure due to improved harvests in southeast Asian countries.

Processed shrimp: Household demand has improved for frozen cooked and prepared shrimp. Usage of pud/p&d, and PTO has also increased at food delivery services; vannamei shrimp sells better due to the price factor. However, demand for sushi shrimp (vannamei) from the Kaiten sushi chains is seriously affected by the slowing restaurant trade.

Import/Export Trade: Lack of real demand in the market have weakened prices of 16/20 counts headless shell-on black tiger shrimp. Japanese buyers’ demand is more for sizes 21/25 and below for which prices are stable as supplies of these sizes are still limited in producing countries. By late May price of Vietnam origin 16/20 fell by US$ 30-50 cents/kg, as shipments consisted more of the large sizes. However, supplies of the preferred mid sizes have improved from this source. But imports from Kolkata (India) packers are affected because of the following the cyclone in late May.

SUPPLY

Myanmar: Black tiger shrimp harvest in Myanmar is forecast to be lower than last year. The farming season has started in April/May but there is very little interest among the farmers practicing semi-extensive aquaculture as the leading market Japan remains unattractive to them. Subsequently black tiger shrimp hatcheries are inactive and many farmers have shifted to soft-shell crab aquaculture. Only extensive farms practising ‘catch and hold’ operations are expected to produce farmed black tiger shrimp this year.

India: As of 1 April 2009, the Government of India has introduced a new ruling which allows only antibiotic-free certified farmed shrimp to be processed for export markets. The authorized laboratories of the Marine Products Export Development Authority of India (MPEDA) will be responsible for checking and certifying according to the required quality (antibiotic-free) standards of farmed shrimp for exports. Meanwhile, in the southwestern shrimp farming belt, many farms producing black tiger shrimp, are getting fully integrated (hatchery/ feed mill/ grow out) to guarantee antibiotic-free harvests.

To meet their Japanese importers requirement, farmers in West Bengal (Kolkata) have started to produce more medium counts (21/25 counts and below) of black tiger shrimp. But in late May, farming in this area has been seriously damaged by the cyclone Aila. High tidal waves, caused damage to 50-60 per cent of the farms and infrastructure and washed away crops which were in the middle of the peak farming season. In southern India, raw material supplies are still lower than expected.

Bangladesh: Black tiger shrimp farms in Khulna/Shatkhira area in Bangladesh are also seriously damaged by the cyclone Aila.

Vietnam: Discouraged by the falling prices of shrimp in the export markets, black tiger shrimp production is scaled down in the southern provinces of Vietnam. As of end March, nearly 8 per cent of the farming area in the country was not prepared for the new season. The most affected provinces are Ca Mau and Bac Lieu where many processing plants are forced to reduce their production by 35-40 per cent. Harvests of black tiger shrimp from this areas are mainly consisted of larges shrimp for which consumer demand is very weak in Japan.

On the converse, there is a surge in farming vannamei shrimp in the southern provinces. This year vannamei production may reach 100 000 MT in Vietnam.

Thailand: Overall production of farmed shrimp dropped 15 per cent during January-March 2009 compared to the same period last year; According to the country’s Shrimp Farmers Association, this year’s production may come down to 392 000 MT compared to 490 000 MT harvested last year. The production cut will be more for vannamei, compared to the black tiger shrimp.

Indonesia: The disease problem occurred in some farming vannamei areas is reportedly under control. Some government sources indicate that overall production may increase by some 20-30 per cent this year. However, with further strengthening of Indonesian Rupiah against the US dollar, current prices in the export market do not compensate the raw material prices. Last year 300 000MT of farmed shrimp were harvested in Indonesia.

IMPORTS

Compared to last year, cumulative imports of shrimp during January-March 2009 increased by three per cent to 566 396 MT against the same period last year. In the coming months, supplies for semi-processed and processed vannamei from Thailand are expected to increase compared to shell-on products. As for black tiger shrimp, market demand for 21/25 and smaller counts will persist.

OUTLOOK

In the international arena, import volume and prices will be largely influenced by the economic situation in the country. Price and convenience will continue to be the key factors affecting consumer demand for the rest of the year in Japan. Consumer spending in Japan has reduced to an extent not witnessed in recent history. However, the increase in home meal preparation is expected to improve household demand for shrimp; semi-processed and processed shrimp will benefit more from this development.

Requisitions from restaurants will be lower than last year due to the downward trends in business. The scheduled marketing plan for the coming summer holiday may also be affected, if the “H1N1 flu” scare prolongs longer.

September 2009

Origins

The fishes’ reproductive behaviour was originally seen as one of its most valuable characteristics, making it unnecessary for small-scale farmers to repeatedly purchase hatchery produced seed, and contributed to its promotion and distribution for rural development purposes throughout the tropics.

The sub-optimal growth and low or variable size (and market value) which mixed-sex populations of tilapia frequently exhibited acted as a constraint to the species commercial development however, leading to efforts in the 1970’s to produce all-male fry in order to circumvent the problem. Despite the obvious promise of such a technical breakthrough no suitable technology for reliably producing all-male tilapia at a commercially viable scale and cost emerged until the mid 1980s.

Development of hapa-based broodstock management, which allowed for collection of tilapia eggs and yolk-sac larvae of a uniform age, proved the key to ensuring consistently high (~99%) levels of male fish following the application for 21 days of feed treated with 17-α methyltestosterone. This breakthrough occurred as a result of doctoral research initiated at the Asian Institute for Technology (AIT) in 1984 as part of an EU funded project on the intensification of septage-fed aquaculture systems. Right; Feeding red tilapia in riverine cages, Ang Thong province.

AIT staff immediately recognised the wider implications of the technology and began to increase production of monosex fry for use in experimental trials, and for sale to forward-thinking commercially oriented fish farmers in Central Thailand who were also quick to grasp the potential of all-male tilapia. Word of the benefits spread rapidly among this group following the publication of articles in local popular media, and the Institute began promotion monosex seed to small-scale farmers in NE Thailand as part of its development focussed extension activities there, as a result of which it expanded hatchery production to a peak of two million per month in early and mid 1990’s.

AIT also worked closely with the Thai Department of Fisheries (DOF) to institutionalise adoption of the technology from the late 1980’s, and established a short course training program for monosex hatchery production as part of its remit for disseminating development focussed research outputs. Short courses attracted more than 100 participants from the public and private sector both locally and internationally but their efficacy initially proved somewhat limited, prompting key staff to seek to extend impacts to the private sector through mentoring and support for, and partnership with, private hatcheries.

Development of the hatchery sector

The first informal partnership began in 1987 with the provision of advice and training to a charitable foundation in Udorn Thani. This facilitated the establishment of a monosex tilapia hatchery to provide a source of income with which the foundation could fund its other rural development activities. Former employees of the foundation operate a hatchery on a similar basis at a different location in Udorn Thani to this day.

1991 saw the birth of a more formal joint venture with an existing hatchery, Rom Sai Farm in Ayutthaya, under which AIT personnel oversaw the construction and operation of a monosex production facility. This was a significant development, increasing the availability of all-male seed in Central Thailand at a key point in the technology’s uptake, but technical and management difficulties ultimately put an end to the collaboration.

In 1993 Manit Farm, a large shrimp and tilapia growout farm in Petchaburi, which had been an early adopter of all-male tilapia seed, established a monosex hatchery of its own after its demand for seed exceeded the production capacity of the AIT hatchery. Again, there were close ties to AIT, and Manit Farm recruited an ex-AIT staff member who had worked at Rom Sai Farm to be its hatchery manager. Manit Farm continues to operate successfully today and is one of Thailand’s leading monosex tilapia seed producers. A year later, in 1994, the farm’s hatchery manager left to establish his own monosex tilapia hatchery and growout business, Boonholme Farm in Khon Kean, which remains one of Northeast Thailand’s foremost seed producers and largest pond-based growout farm.

A subsequent joint venture between AIT, a subsidiary company of Cargill, and two local entrepreneurial investors resulted in the startup of Nam Sai Farm in Prachinburi Province in 1994. The company was headed by the former AIT-employed hatchery manager from the earlier venture in Ayutthaya under an agreement by which AIT would provide technical support and expertise for a six year period, receiving a royalty fee from the Cargill subsidiary for each fish produced. Following the end of this arrangement Nam Sai continued as one of the largest monosex hatcheries in the country.

Charoen Phokpand (CP), the Thai agro-industrial giant, initiated commercial production of all-male tilapia seed in 1995 following several years of experimentation. Again, a fairly direct line of technology transfer can be traced to AIT, with CP staff attending short course training there and AIT alumni joining the company’s aquaculture division, but close personal ties played a less critical role than in the earlier start-ups. CP now operates five tilapia hatcheries around the country and produces more all-male tilapia fry than the country’s next three largest monosex hatchery operators combined.

From the late 1990’s onwards the number of monosex hatcheries in Thailand proliferated (to well in excess of 20 at present), as farmer demand for sex-reversed fry increased and knowledge of the necessary hatchery management techniques, once confined largely to individuals associated with the early development of the technology at AIT, became more widely accessible. Knowledge transfer through DOF officers came to play an increasingly important role; mainly by consultancy and advice given unofficially as part of close relationships between hatchery operators and DOF staff. At least three monosex hatcheries were established in this manner, most notably Bor Charoen Farm in Chachoengsao, which is now one of the largest, and certainly the most technologically advanced in the country. In other instances ex-staff of hatcheries including Nam Sai and CP left to start businesses of their own, and several fry agents who had established a customer base by nursing and selling fingerlings for cage culture used this as an entry point into hatchery production.

Although DOF produces small numbers of monosex fry at fisheries research stations throughout the country for use in extension activities and for sale to small-scale farmers and nursing co-operatives it’s most significant contribution by far, aside from the unofficial role described above, has been the provision of high quality broodfish to hatchery owners. At present only four hatchery operators possess the capacity to develop broodstock independently, with the vast majority of the remainder reliant on the government run Aquatic Animal Genetics Research and Development Institute for this service.

Table 1: Name, lodation, date established, knowledge acquistion pathway, and estimated average monthly fry sales for monosex tilapia hatcheries in Thailan

The ability to produce all-male tilapia fry has revolutionised the profile of the species’ production and consumption in Thailand in the last 15 years, bringing about huge changes in productivity, profitability, value, and diversification. The following sections describe associated developments in two distinct sectors; pond and cage culture.

Pond culture

Thai tilapia production has increased, almost exponentially, from an officially recorded 22,800t in 1990 to 203,700t in 20051. This growth can by no means be exclusively attributed to monosex; the advent of improving transport and communications, greater access to agricultural by-products for use as feeds and fertilisers in pond culture, and the increasing size and affluence of urban markets, being critical factors2. However, the existence of tilapia capable of quickly, reliably, and cost efficiently reaching larger sizes (400g-1kg; as opposed to the 250-350g at which mixed sex tilapia were typically harvested) has radically altered the species’ utility to farmers and led to major shifts in marketing strategies and consumer preferences.

Production of cyprinid species – once the mainstay of greenwater polyculture systems that predominated in Thailand – has, with the exception of silver barb (Barbodes gonionotus), all but stagnated over the same period. This far slower rate of growth can be substantially attributed to the progressive dominance of monosex tilapia in pond polyculture. Greenwater polyculture systems in central Thailand are now typically comprised of around 90% monosex tilapia, with assorted carp species (which attract a somewhat lower market value) stocked to fill vacant ecological niches in the pond in order to help maintain water quality.

Farmers stocking monosex tilapia in ponds tend to pursue one of two broad production and marketing strategies. The first, more traditional, system is generally practiced by smaller and medium scale farmers (with holdings in the order of 20-100 rai), in which growout periods of around 8 months facilitate production of tilapia averaging 400-500g. These fish are stored on ice upon harvest, and distributed to fish markets in Central, and to a lesser extent, NE Thailand, and attract a farmgate value in the order of Bt18-20/kg.

Larger farms (100 to >1,000 rai) typically focus on the production of tilapia averaging upwards of 600g. Total growout cycles can last 12-13 months, with partial harvest (thinning out for sale or restocking in other ponds) occurring on two or three occasions, allowing remaining fish to rapidly gain weight. Formulated pellet feeds may be fed during the later stages of growout to assist fattening. Fish are placed in aerated tanks upon harvest for distribution to local markets where they are sold live to demonstrate product freshness to consumers. Large live tilapia attract a considerably higher farmgate price than their dead counterparts (~Bt30/kg).

Production in this manner has become increasingly common in the last five years and now accounts for perhaps 40% of the output of pond culture from the Central region, but is generally only practiced by farmers with sufficient knowledge, experience and space to carefully manage all aspects of growout and staggered harvesting, and with sufficient capital to enable them to defer returns on investment for a year or more. A great many of these originate from a handful of districts in southern Bangkok and Samut Prakan province where commercially oriented pond culture has been widely and successfully practised for over 30 years. These entrepreneurial individuals have expanded operations into provinces including Prachinburi, Nakorn Nayok, Chachoengsao and Ratchaburi where affordable land and labour are more readily available than inside the heavily urbanised Bangkok Metropolitan Region.

Cage culture

The development of pond culture post-monosex can be seen a largely organic affair, resulting from a gradual evolution led by innovative farmers and actors in the marketing chain, and confined primarily to provinces in central Thailand where abundant water, land and feed resources exist. In contrast, the origins of cage-based tilapia culture (which now accounts for perhaps 30% or more of the total output of Thai tilapia) can be traced directly to the research, development and marketing activities of a single corporate entity; CP. The dominant force in Thai agro-industry, CP was already the prime mover in the country’s shrimp industry and a major supplier of feed for walking catfish (Clarius sp.) culture at the point when monosex hatchery production techniques emerged. Initially focussing on production of tilapia for a buoyant export market, CP began experimenting with the development of saline tolerant strains of hybrid (Oreochromis sp.) red tilapia for culture in vacant shrimp ponds on the upper Gulf of Thailand. Although these efforts ultimately proved unsuccessful, in part due to the slow growth of tilapia under these conditions, the company switched its attention to the application of these research outputs to the domestic market. Left: Farmers must share the river with many other users.

The enhanced feeding efficiency of monosex over mixed-sex tilapia (FCRs for cage culture averaging around 1.4 and 1.8 respectively), and the larger size and, hence, value attainable, made the prospect of production based exclusively on formulated diets an economically viable possibility for the first time. Adapting the existing concept of cage-based culture to suit its needs, the company launched a concerted marketing strategy based on a shrewd assessment of regional fish consumption preferences, with the ultimate goal of expanding its market for aquatic feeds.

The company promoted sales of live tilapia through television advertisements, endorsements from high profile chefs, product dumping in markets at below production cost, and the engagement of restaurants and caterers providing set meals at festivals and celebrations. CP’s marketing in central Thailand revolved primarily around a red strain of tilapia (named pla tabtim by the King of Thailand), reflecting a need to differentiate the product from smaller, dead, pond-produced Nile tilapia commonly considered by Thai consumers to be of low quality due to the frequent occurrence of off-flavour. In the N and NE of the country, where pond raised tilapia are far scarcer and live fish are highly sought after, large live Niles proved more compatible with local tastes.

Cage culture of both red and Nile tilapia (based on a contract farming system under which feed and fry produced by the company are supplied to farmers through a network of affiliated dealerships which buy back and market live fish when they attain at a weight of 600g or more) expanded dramatically as a result. Cage-raised fish are now by far the most significant source of tilapia in markets in the northern part of the country, whilst in the central region cage production is limited almost exclusively to red strains. The extent of this division is illustrated by CP’s hatchery output, around one third of which is red and marketed largely in Central provinces, with the remaining two thirds of Nile tilapia fry destined primarily for growout in cages in rivers and reservoirs in the N and NE. This live marketing of fish may also have had unforeseen spill over effects on the development of pond culture, setting a precedent from which the increasing popularity of live pond-produced tilapia described above followed.

CP’s initiative (which is better viewed as an exercise in astute marketing than a major technical advance) has radically influenced the scale and form of tilapia production in Thailand. However, the system - which transfers risks associated with distribution of feed, seed and final product on to its dealerships and, ultimately, cage farmers, allowing the company to pursue capital accumulation via the profitable feed production arm of the business – is typically a less secure proposition for end users than independently developed pond-based production strategies.

That CP now controls perhaps 60% of the production system it created around 10 years ago testifies in part to the less than charitable practices of certain dealerships working under the company (among a range of complaints voiced by farmers, a failure to honour agreements pertaining to the farmgate value of harvested fish and excessively high input costs are some of the most common). The remainder of the market is divided up between several feed companies operating similar ‘integrated’ informal contract systems and farmers producing and marketing fish on an independent basis.

The future of cage-based tilapia production looks increasingly uncertain however; the open nature of cage systems and their location in water bodies impacted by multiple users rendering them vulnerable to a range of adverse environmental factors including pollution episodes, low water levels and/or flow rates (particularly in rivers and reservoirs in the NE), annual flooding events and highly turbid water and, perhaps most critically, disease.

Based on anecdotal reports it appears that the incidence of disease in cage-raised tilapia has become increasingly more severe in the last two years. Annual outbreaks of Streptococcus during the hot dry season have occurred regularly for some time, but these appeared to have been augmented recently by serious parasitic infections and a new and particularly virulent pathogen, possibly Microsporidium which was apparently responsible for very substantial mortalities in April and May of this year.

Current trends and future directions

Cage-based tilapia production now appears increasingly unsustainable from the farmer’s perspective in light of progressively more severe disease problems and water quality and availability issues coupled to the rapidly rising cost of commercial feeds. The alternative, which several particularly well informed interviewees suggest is likely to occur within the foreseeable future, is a comprehensive shift from cage culture in multi-use water bodies to intensive cage-based production in aerated ponds; the latter requiring greater capital investment but far being less vulnerable external environmental pressures. A small number of farmers already practise similar culture techniques, nursing Nile tilapia to 200-300g at high density in greenwater before transferring to cages in ponds for rapid fattening on high quality pellet feeds. White shrimp (Litopenaeus vannamei) and giant freshwater prawn (Macrobrachium rosenbergii) are also stocked in these ponds at low density to provide an additional high value crop.

Numerous other tilapia farmers have also begun stocking shrimp and/or prawn as an additional species and, inversely, it is now commonplace for inland shrimp and prawn farmers to stock tilapia in their systems. In both instances this development appears to be a response to declining profit margins (in the case of tilapia farmers this is due to inflationary pressure on feedstuffs which modest increases in the market value of the fish had been unable to make up for), and has the added benefit of providing some measure of biological control through the removal of detritus and uneaten feeds.

Record prices for Thai rice earlier this year have also brought about some unexpected changes. In one district of Nakorn Pathom, and almost certainly in other areas, a number of small-scale but marginally successful tilapia farmers have, temporarily at least, abandoned pond culture in favour of rice production which is, under normal circumstances, a far lower income activity. In addition it appears that associated increases in the value of rice bran, the most widely used supplementary feed among farmers operating traditional greenwater growout, have made the substitution of low protein formulated feed an economically viable alternative pond input due to the trade-off in reduced growout periods which it facilitates. Whether these trends are likely to continue if rice prices return to more normal levels is open to question, but they underline clearly the intimacy with which fish culture in Central Thailand is bound to other agricultural activities.

Recorded tilapia exports from Thailand are currently fairly meagre (5,128 t in 2006). This figure may under-represent the real volume, considering that national statistics for total tilapia output almost certainly under-report total annual output. However, the likely prospects for expansion of export-led tilapia production remain uncertain. Whilst there may be potential for expansion of Thai exports given the species’ ever greater importance as an internationally traded commodity, Thai producers apparently experience difficulties in competing with those in China for a variety of reasons which may include comparative advantages in the cost of feed production and labour, Chinese government export subsidies, and total production volumes. Perhaps the most significant reason for the failure of the sector to expand to date is that domestic consumption has kept pace with production increases. This has meant that local market values are currently comparable to those for export, providing little incentive to producers to pursue these more demanding markets. However, as production continues to expand and intensify, facilitating the production of greater volumes of consistently large, high quality fish, better capitalised Thai producers may ultimately find it advantageous, and even necessary, to enter the global marketplace in order to dispose of their product.

Acknowledgements:

The authors would like to acknowledge the generous support and assistance provided by AIT’s EU funded Asia-Link Aqua Internship program, Warren Turner and Termsac Kongsamran, and all of the farmers, hatchery operators and other individuals who gave their time in contributing to the research that facilitated the writing of this article.

References

DOF. 2007. Fisheries Statistics of Thailand 2005. Department of Fisheries, Ministry of Agriculture and Cooperatives, Bangkok, Thailand.

Belton, B. and D. C. Little. 2008. The Development of Aquaculture in Central Thailand: Domestic Demand versus Export-Led Production. Journal of Agrarian Change. 8 (1): 123-143.

This article was published in Aquaculture Asia Magazine

August 2009