Assignment on Shrimp Culture in Bangladesh

Introduction: Modern shrimp farming, the production of marine shrimp in impoundments, ponds, raceways and tanks, got started in the early 1970s, and, today, over fifty countries have shrimp farms. In the Eastern Hemisphere, Thailand, Vietnam, Indonesia, India and China are the leaders, and Malaysia, Taiwan, Bangladesh, Sri Lanka, The Philippines, Australia and Myanmar (Burma) have large industries. In the Western Hemisphere, Mexico, Belize, Ecuador and Brazil are the leading producers, and there are shrimp farms in Honduras, Panama, Colombia, Guatemala, Venezuela, Nicaragua and Peru. The shrimp importing nations–the United States, Western Europe and Japan–specialize in high-tech “intensive” shrimp farming (more about this below), but, thus far, their production has been insignificant. In the Middle East, Saudi Arabia and Iran produce the most farmed shrimp.

Shrimp farms use a one-phase or two-phase production cycle. With the two-phase cycle, they stock juvenile shrimp from hatcheries in nursery ponds and then, several weeks later, transfer them to grow out ponds. With the one-phase cycle, the nursery ponds are eliminated, and the shrimp are stocked directly into grow out ponds, after having spent a short period in acclimation tanks (more below). Farms usually produce two crops a year, although farms within 10 degrees of the equator sometimes get three crops a year.

Hatchery

Hatcheries sell two products: nauplii (tiny, newly hatched, first stage larvae) and post larvae (which have passed through three larval stages). Nauplii are sold to specialized hatcheries which grow them to the post larval stage.

The Hatchery Cycle:

 Whether gravid (ready-to-spawn) shrimp are captured in the wild or matured in the hatchery, they invariably spawn at night, but with photoperiod manipulation, they can be induced to spawn at any time. Depending on a number of variables (temperature, species, size, wild/captive and number of times previously spawned), they produce between 50,000 and 1,000,000 eggs. After one day, the eggs hatch into nauplii, the first larval stage. Nauplii, looking more like tiny aquatic spiders than shrimp, feed on their egg-yoke reserves for a couple

of days, and then metamorphose into zoeae, the second larval stage, which have feathery appendages and elongated bodies but few adult shrimp characteristics. Zoeae feed on algae and a variety of formulated feeds for three to five days and then metamorphose into myses, the third and final larval stage. Myses have many of the characteristics of adult shrimp, like segmented bodies, eyestalks and shrimp-like tails. They feed on algae, formulated feeds and zooplankton. This stage lasts another three or four days, and then the myses metamorphose into post larvae. Post larvae look like adult shrimp and feed on zooplankton, detritus and commercial feeds.

Farmers refer to post larvae as “PLs”, and as each day passes, the stages are numbered PL-1, PL-2, and so on. When their gills become branched (PL-13 to PL-17), they can be moved to the farm. From hatching, it takes about 25 days to produce a PL-15.

Small-Scale Hatcheries:

 Hatcheries come in three sizes: small, medium and large. Small-scale hatcheries are usually operated by a family group on a small plot of land. Called “mom-and-pop” or “backyard” hatcheries, they adopt a green-thumb, non-technical approach. Their chief advantages: low construction and operating costs and the ability to open and close, depending on the season and market factors. They utilize small tanks (less than 10 tons) and concentrate on just one phase of production, like nauplii or post larvae production. They often use low densities and untreated water. Diseases, the weather and water quality problems often knock them out of production, but they can quickly disinfect and restart operations. Survival of the developing larvae in small-scale hatcheries ranges from zero to over 90%, depending on a wide range of variables, like stocking densities, temperature and the experience of the hatchery operator. Small-scale hatcheries have achieved great success in Southeast Asia, particularly in Thailand, Taiwan, Indonesia, the Philippines and southern China. In Thailand, which has thousands of backyard hatcheries, the industry is segmented into suppliers of nauplii, post larvae, phytoplankton, equipment, feeds and chemicals.

Medium-Scale Hatcheries:

 Most medium-scale hatcheries are based on a design developed in Japan and popularized by the Taiwanese. Called “Japanese/Taiwanese”, “eastern” or “green water” hatcheries, they use large tanks, low stocking densities, low water exchange and encourage an ecosystem to bloom within the tank. This bloom feeds the developing shrimp. In some cases, various nutrients and bacteria are added to the tanks which discourage the growth of “bad” bacteria and encourage the growth of “good” bacteria (probiotics). This ecosystem approach is supposed to produce stronger post larvae due to its closer approximation of natural conditions and the absents of therapeutics. Survival, from stocking to harvested post larvae, is usually 40%, or less.

Large-Scale Hatcheries:

 These are multimillion-dollar, high-tech facilities that produce large quantities of seed stock in a controlled environment. Originally developed at the Galveston Laboratory of the United States National Marine Fisheries Service, they are referred to as “Galveston”,

“Western” or “clear water” hatcheries. Requiring highly paid technicians and scientists, they utilize big tanks (15 to 30 tons), filtered water, high densities, and high rates of water exchange, allowing them to take advantage of the economy of scale by producing seed stock throughout the year. They grow algae and brine shrimp and feed them to the developing shrimp. High survivals, up to 50%, are common with these systems, though in practice survivals range from zero to 80%.
In the Western Hemisphere, big hatcheries are the established trend, but large-scale hatcheries can also be found in all the major shrimp farming countries.

Many large-scale hatcheries maintain captive brood stock in “maturation facilities”, which require expensive live feeds like bloodworms, squid, bivalves and other crustaceans (adult Artemia and krill). Dry formulated feeds are not as popular because they don’t work on a 100% replacement basis.

Since Penaeus vannamei (the most popular species in the Western Hemisphere) is easier to work with than P. monodon (the most popular species in the Eastern Hemisphere), captive breeding is more common in the west than the east. Most breeding facilities recirculate the water in the broodstock tanks, creating a closed system where water quality variables can be controlled and external factors limited.

Hatchery Feeds:

Hatcheries utilize a combination of live feeds, such as microalgae and brine shrimp nauplii (Artemia), with one or a number of prepared diets, either purchased commercially or prepared at the hatchery. The principal algal species employed is Chaetoceros muelleri. Again, dry formulated feeds are popular, but they don’t work on a 100% replacement basis.

Eighty percent of the hatcheries in the Western Hemisphere use some artificial broodstock diets. In 15% of the hatcheries, artificial diets represented more than 25% of the total feeding regime. Hatcheries used Breed S (INVE Aquaculture NV, Belgium), Higashimaru (Higashimaru Co., Japan), MadMac MS (Aquafauna Biomarine, Inc., USA), Nippai (Japan), Rangen (Rangen, Inc., USA) and Zeigler (Zeigler Bros., Inc., USA).

Shrimp nauplii stop feeding on their yolk reserves when they molt into the zoea stage. In nature, the zoea and following mysis stage feed on microalgae or a combination of microalgae and zooplankton. In shrimp hatcheries, live food is provided throughout these early larval stages to improve survival and growth. The biological value of live food cannot be entirely explained by analyzing its biochemical composition. This special value is referred to as the “live food factor”, which could be nutritional components, enzymes, attractants, hormones, antimicrobials, or something else. It may result from better utilization of key nutrients that avoid the rigors of double processing. A higher inclusion rate of fresh and fresh-frozen marine protein ingredients in larval diets reduces the dependence on cultured microalgae and Artemia cysts.

The proceedings of the shrimp farming sessions at World Aquaculture 2003 in Salvador, Brazil (May 2003), contains a great paper on shrimp hatchery feeds. Some excerpts:

Liquid feeds are a slurry of particles in suspension. A 2001 survey reported that approximately 50% of shrimp hatcheries used liquid feeds to feed larval shrimp. Although expensive, they cause less fouling and can be continuously dosed into larviculture tanks using peristaltic pumps. Given their high moisture content (60 to 70%) and low levels of protein (around 3%) and lipids (around 2%), liquid feeds aim primarily to be carriers for probiotics, vitamins, minerals and other solubles.

Hatcheries feed Artemia nauplii nutrients and medicines and then feed those nauplii to larval farm-raised shrimp–and the nutrients and medicines are passed on to the shrimp. The Artemia naups can be spiked with bactericides to reduce the bacterial loads during hatching and holding.

Freeze-drying (lyophilization) removes water from frozen products without having to thaw them first. The process of freeze-drying is considered to be the most conservative and safe method for drying and preserving fragile nutrients.

Because of their large size (800um in length), freeze-dried arctic crustaceans (Cyclop-eeze®) could only be fed to late stage P. monodon postlarvae. Source: Responsible Aquaculture for a Secure Future. The Proceedings of a Special Session on Shrimp Farming at World Aquaculture 2003 (Bahia, Brazil, May 2003). World Aquaculture Society. Edited by Darryl Jory. Larval shrimp feeds: Current status. Roeland Wouters and Tille Van Horenbeeck (INVE Technologies, NV, Hoogveld 93, B-9200 Dendermonde, Belgium.

Hatchery Trends:

 In the Western Hemisphere, hatcheries are usually very large and often associated with big farms. They frequently supply nauplii to smaller hatcheries in other regions and other countries. The smaller hatcheries raise the nauplii to post larvae, which are sold to farms for stocking in nursery or grow out ponds. Many of the large centralized hatcheries breed shrimp for special characteristics, like rapid growth and disease resistance.

In the United States, specific pathogen-free (SPF) seed stock has demonstrated great potential. Prior to the arrival of the Taura virus in 1995, industry production doubled when the SPF stocks were introduced. Unfortunately, the SPF stocks of P. vannamei were extremely sensitive to the Taura virus, and the U. S. industry suffered major losses in 1995.

In the Eastern Hemisphere, small and medium-scale hatcheries continue to produce most of the seedstock. Worldwide, the once clear distinction between Japanese/Taiwanese-style and Galveston-style hatcheries is increasingly blurred as a large number of hybrid operations, borrowing the best from both, are adapted to local conditions and experience. The advent of the backyard hatchery has further blurred the distinction. Success has not been the exclusive domain of any one style, and it is becoming more and more obvious that hatcheries must be adapted to local conditions.

Nursery:

The nursery phase of shrimp farming, when post larvae are cultured at high densities in small earthen ponds, tanks and raceways, or even in enclosures within the grow out ponds, occurs between the hatchery and grow out phases. Since hatchery-produced and wild-caught post larvae can be stocked directly into grow out ponds, the nursery phase is not always necessary.

Farmers stock post larvae in nursery ponds (0.5 to 5.0 hectares) at densities of 150 to 200 per square meter and feed a crumbled diet several times a day. Protein levels in these feeds range from 30 to 45%. The nursery phase should not exceed 25 days.

Proponents of nurseries argue that they improve inventory, predator and competition control; increase size uniformity at final harvest; better utilize farm infrastructure; permit more crops per year; improve risk management; produce stronger post larvae; and decrease feed waste. Because low salinity levels can be lethal to post larvae, nurseries also provide a halfway house where salinities can be adjusted to pond levels.

The main criticism of nursery systems is that post larvae suffer mortalities when they are transferred to grow out ponds. Spontaneous mortalities also occur in nursery ponds when animals are held beyond 25 days.

Nurseries in greenhouses find applications in temperate climates where it is important to get a jump on the grow out season.

At Aquaculture 2004 (Hawaii, USA, March 1–5, 2004), I chatted with Bill More about a nurseries. Bill More has been farming shrimp in the Western Hemisphere for thirty-six years. Currently, with his wife Betty, he runs More & More Consulting Services, Inc., which has recently done work in Mexico and Central America. Bill also serves as vice president and director of the Aquaculture Certification Council, which is a process certification program for shrimp farms, processing plants and hatcheries and soon feed mills.

Shrimp News: You also mentioned renewed interest in nursery systems and a trend away from acclimation tanks. What’s going on there?

Bill More: That’s right. In the early days, shrimp farmers had a lot of success with nursery ponds, but with the onset of all the virus problems (especially Taura) in the early 1990s, survivals in nursery ponds began to drop, and many were abandoned in favor of acclimation tanks. Now, as we put some of the virus problems behind us, several farms have found it profitable to stock with juveniles from nursery ponds because survivals in nursery ponds have jumped from 25% to 75%. This is especially true for the first crop of the season.

Shrimp farmers used to hold animals in nursery ponds for 30 to 60 days; now they try to move them into grow out ponds in less than 30 days (at 0.5 to 0.8 grams each). This reduces stress on the animals and dramatically increases survivals in the grow out ponds. Many farms in Honduras that abandoned nursery ponds have gone back to them, and the results have been surprisingly positive. They’re using the old, uncovered, earthen, nursery ponds.

Another trend is the head-start, raceway nursery, like those in Mexico, which are covered to conserve heat. Since their primary purpose is to get a jump on the season, they hold the post larvae for about 28 days and then move them to grow out ponds at less than a gram each. Then they restock the raceways. A few intensive raceways can stock a lot of ponds.

Many intensive raceway nursery systems have also been built in Ecuador. Even in Ecuador, the raceways are covered because nighttime temperatures drop enough to cause problems, especially during the dry season. Some of these systems run at 35°C for up to 45 days without white spot. They produce large (a little less than two grams), white spot-free, stress-free juveniles–which doesn’t mean they won’t get white spot, but it does mean their chances of survival are much greater than stocking PLs directly in the ponds.

Belize is also beginning to implement raceway nursery systems. Like Mexico, it has a shorter growing season and likes to get a jump on the season by starting the animals in nurseries.

One of the reasons for the trend back to nursery ponds has to do with farmers’ attempts to produce larger animals. Information: Bill More, More & More Consulting Services, Inc., 12815 72nd Avenue, Northeast, Kirkland, WA 98034 USA (phone 425-825-8634, fax 425-671-0146, email wrmore@comcast.net, webpage http://www.aquaculturecertification.org/index/).

Acclimation Tanks:

 In the Western Hemisphere, acclimation tanks, pond-side facilities for receiving and conditioning post larvae, are being replaced by nurseries, which produce larger post larvae for stocking.
But acclimations have some advantages: Since they’re on top of the pond banks, or higher, it’s easy to transfer seed stock to ponds. They make it easy to observe and evaluate incoming seed stock, which can be fed special diets to prepare them for the rigors of pond life. They make great holding facilities while ponds are being harvested, or while a storm passes overhead. They give the seed stock a chance to adjust to pond conditions, particularly salinity and temperature before stocking. And they don’t have to be next to the ponds. For example, they can be on the hatchery grounds where it’s easier to control water quality and feeding.
The most important consideration during acclimation is that the water quality parameters be changed slowly. Acclimation densities should not exceed 300-500 post larvae per liter, depending on animal size and duration of acclimation.

Grow:

Once a grow out operation is stocked with post larval shrimp, it takes from three to six months to produce a crop of market-sized shrimp. Northern China, the United States and Northern Mexico produce one crop per year; semi-tropical countries produce two crops per year, while farms closer to the equator have produced three crops a year, but rarely. Temperature has a lot to do with it. Shrimp like it hot, and most species prefer, but are not restricted to, brackish water.

Grow out operations come in all shapes and sizes. They are classified by stocking densities (the number of seed stock per hectare) and called “extensive” (low stocking density), “semi-intensive” (medium stocking density), “intensive” (high stocking density) and “super-intensive” (highest stocking density). As densities increase, the farms get smaller, the technology gets more sophisticated, capital costs go up and production per unit of space increases dramatically.

Extensive:

 Extensive shrimp farming (low-density) is conducted in the tropics, in low-lying impoundments along bays and tidal rivers, often in conjunction with herbivorous fish. Impoundments range in size from a few hectares to over a hundred hectares. When local waters are known to have high densities of larval shrimp, the farmer opens the gates, impounds the wild larvae and then grows them to market size. Fishermen also capture wild post larvae and sell them to extensive farmers for stocking. Overall, however, stocking densities are quite low, not over 25,000 post larvae per hectare. The tides provide a water exchange rate of from 0 to 5% per day. Shrimp feed on naturally occurring organisms, which may be encouraged with organic or chemical fertilizer. Construction and operating costs are low and so are yields. Cast-nets and bamboo traps produce harvests of 50 to 500 kilograms (head-on) per hectare per year.

Semi-Intensive:

 Conducted above the high tide line, semi-intensive farming introduces carefully laid out ponds (2 to 30 hectares), feeding and pumping. Pumps exchange from 0% to 25% of the water a day. With stocking rates ranging from 100,000 to 300,000 post larvae per hectare, there is more competition for the natural food in the pond, so farmers augment production with shrimp feeds. Wild or hatchery-produced posts larvae are stocked in grow out ponds which are fertilized (nitrogen, phosphorus and silicate) to encourage a natural food chain. The farmer harvests by draining the pond through a net, or by using a harvest pump. Yields range from 500 to 5,000 kilograms (head-on) per hectare per year. Farmers usually renovate their ponds once a year. If too many semi-intensive farms concentrate in a small area, they can have a negative effect on the environment.

Intensive:

 Intensive shrimp farming introduces small enclosures (0.1 to 1.5 hectares), high stocking densities (more than 300,000 post larvae per hectare), around-the-clock management, heavy feeding, waste removal and aeration. Aeration–the addition of air, or oxygen, to the water–permits much higher stocking and feeding levels. The water exchange rate can be high, 30% per day and up. Frequently conducted in small ponds, intensive farming is also practiced in raceways and tanks, which may be covered or indoors. Sophisticated harvesting techniques and easy pond clean-up after harvest permit year-round production in tropical climates. Yields of 5,000 to 20,000 kilograms (head-on) per hectare per year are common. The effluents from intensive farms frequently cause environmental problems.

Super-Intensive:

Super-intensive shrimp farming takes even greater control of the environment and can produce yields of 20,000 to 100,000 kilograms per hectare per year! Thailand has some super-intensive shrimp farms. A super-intensive farm in the United States once produced at the rate of 100,000 kilograms (whole shrimp) per hectare per year, but it was wiped out by a viral disease. Belize Aquaculture, Ltd., one the most advanced shrimp farm in the world, uses super-intensive production techniques. It and farms like it around the world encourage bacterial flocks to develop in their super-intensive ponds. The flocs remove nitrogenous waste products from the water, and the shrimp feed on the flocks! Since production costs per kilo are low, these systems have sparked considerable interest and probably represent the future of shrimp farming.

Farming Strategies:

 Although almost all of the shrimp farms built in the last few years have been semi-intensive and intensive, much of the world’s production still comes from extensive farms. India, Vietnam, Bangladesh, the Philippines and Indonesia are good examples of countries that have extensive farms. Ecuador and Honduras have extensive farms. China pursues its own brand of intensive farming. Japan, Taiwan and the United States concentrate on intensive shrimp farming–and intensive farms occur in all the major shrimp farming areas of the world.

Factors Affecting Production Feeds:

 As farms evolve from low to high stocking densities, the quality of feed becomes very important. Most extensive farms (low stocking densities) don’t feed at all; shrimp feed on naturally occurring food organisms in the pond. Other extensive farms use small amounts of feed and fertilizer to stimulate a natural food chain. On semi-intensive farms, with many more shrimp scouring the bottom of the ponds, most of the feed is consumed by the shrimp and less is available to serve as a stimulant to the natural food web. Therefore, the quality of the feed is more important because the shrimp get most of their nutrition from it. On super-intensive farms, where bacterial flocs develop, the shrimp graze on the flocs, so the protein levels in the feeds can be reduced.

Ideally, shrimp in semi-intensive and intensive farms should be fed four or five times a day, with at least three hours between feedings. High-quality feeds offer several advantages over lower quality feeds: better feed conversion, faster growth, lower mortalities and improved water quality. In 2005, feed mills around the world produced approximately two million metric tons of shrimp feed. All things considered, including the abysmal state of shrimp farming statistics, that figure probably increased in 2006, along with increase in shrimp production.

Feeds can represent over 50% of the production costs on intensive shrimp farms, and they make a mighty contribution to the sludge on the bottom of the pond. Consequently, shrimp farmers believe better feeds and feeding strategies could save them a lot of money. The shrimp’s habit of slowly nibbling feed particles causes substantial nutrient losses even if the pellets are of good quality. Increasing the water stability of the feed beyond a couple of hours does not help, because leaching of the nutrients will continue, even from pellets showing excellent physical stability. Within an hour, shrimp feed can lose more than 20% of its crude protein, about 50% of its carbohydrates and 85 to 95% of its vitamin content. As much as 77% of the nitrogen and 86% of the phosphorus compounds in shrimp feed are wasted. The waste either accumulates on the pond bottom, or is discharged into the environment. Instead of increasing pellet stability beyond a couple of hours, feeds should include attractants so they are consumed within 20 or 30 minutes.

Because the Asian shrimp feed market is highly competitive, most feed manufacturers produce feeds with excessive nutrient levels to assure that their products are well received in the marketplace. Consequently, shrimp feeds tend to contain a considerable volume of fishmeal, usually 30 to 35% of the total. In those countries that produce shrimp extensively–Indonesia, India, Philippines, Vietnam and Bangladesh–farmers utilize feeds with lower protein and fishmeal levels.

Farmers in the Western Hemisphere depend almost entirely on dry, commercial feeds, while 50% of those in the Eastern Hemisphere utilize farm-made feeds and natural foods, such as trash fish, seafood by-products and various mollusks and crustaceans, a practice which can encourage the spread of disease and adds to the organic load in the pond.

Feeding Trays:

Most shrimp farmers broadcast feeds from the pond bank or from small boats. Then they lower feeding trays–small (about 1/2 square meter), circular or rectangular, mesh-bottomed baskets containing feed–into the pond to monitor consumption. In 1992, shrimp farmers in Peru began using feeding trays to feed the entire pond. They distribute the trays around the pond so that each one “feeds” an area of approximately 500 to 1,000 square meters. Labor costs are high with this technique. At least two employees are required for every 10 hectares of ponds. But, because feed conversion ratios are so much lower when feeding trays are used, labor, construction and equipment costs are easily covered by reduced feed costs. In addition, feeding trays offer the following advantages:

•           Less pollution and cleaner pond bottoms
•           Reduced stress, fewer disease problems and faster growth
•           An invaluable source of data on what is going on in the pond
•           Early detection of disease
•           Controlled administration of medicated feeds
•           Reduced pumping and aeration costs
•           Less pond maintenance between harvests
•           Better harvest estimates

At Aquaculture 2004 (Hawaii, USA, March 1–5, 2004), I chatted with Bill More (above) about feeding trays.

Shrimp News: You mentioned the broad acceptance of feeding trays in the Western Hemisphere. What’s the current status of their use?

Bill More: The trend started in Peru in the early 1990s and has now spread to Guatemala, Brazil and Mexico–actually, you see feeding trays at many of the large, semi-intensive farms and most of the intensive farms in the Western Hemisphere. When one shrimp farmer observes another shrimp farmer having success with a new technology, that technology spreads quickly from farm to farm and country to country. Shrimp farmers can reduce their feed conversion ratios from around 2:1 down to 1.3 to 1.4:1 with feeding trays. That’s a significant reduction!

But they’re labor intensive! Two people can pull 100 to 200 trays per hour. When you have 15 to 20 trays per hectare and four feedings a day, that’s a lot of tray pulling.

Shrimp News: Give me a little rundown on the utilization of feeding trays in Latin America.

Bill More: With the recent success that Honduras and Guatemala have had in coming back from white spot, some farms have increased stocking densities to 15 to 20 per square meter and higher in intensive ponds with aeration. Many of these operations are switching over to trays, and in the last six months of 2003, many of those farms experienced the same success that other tray users have experienced. Initially, they feed a few ponds with trays, but once they see the results, they feed all their ponds with trays.

Countries like Panama, Nicaragua and Ecuador that have traditionally stocked at lower densities are not using trays. Most farms that stock fewer than 10 post larvae per square meter do not use trays.

Colombia is beginning to use feeding trays.

Brazil uses lots of feeding trays because its farms stock at high densities and feeding trays appear to provide their biggest benefit in high-density ponds.

Shrimp News: Where are the shrimp farmers getting their feeding trays?

Bill More: Most farms make their own with weighted-down PVC pipe and cheap screening material, some are round, some square and some rectangular. They cost from $2.50 to $5.00. The screen lasts for a year or two, and the frames can last for up to four years. For one reason or another, about 50% of the trays have to be replaced every year, so on a large farm, trays are a sizeable investment. Information: Bill More, More & More Consulting Services, Inc., 12815 72nd Avenue, Northeast, Kirkland, WA 98034 USA (phone 425-825-8634, fax 425-671-0146,).

Aeration:

Shrimp farmers use tidal flow and diesel pumps to maintain stable water quality conditions and to renew the dissolved nutrients that sustain healthy algal blooms in their extensive and semi-intensive ponds. This process introduces freshly oxygenated water and helps flush out wastes. To further increase oxygen levels, some semi-intensive farms and most intensive farms use paddlewheel and aspirating aerators, electrical/mechanical devices that add oxygen to the water. They are used at night and early in the morning when oxygen levels are at their lowest. Paddlewheels slap, beat and churn oxygen into the surface of the water; aspirators inject an oxygen-rich stream of water below the surface. Shrimp flourish in the currents created by the aerators. Paddlewheel aerators have many moving parts and a lot of down time; aspirators have few moving parts. Producers of paddlewheel and aspirating aerators actively compete for the intensive shrimp farmer’s business. Since the costs are similar, neither technology has established itself as better than the other.

Blower-type aerators (low-pressure air), a third technology, deliver air to the bottom of the pond through a network of pipes and tubes. These simple, non-mechanical systems can be maintained with unskilled labor. Less popular than paddlewheels and aspirators, they find applications in hatcheries and in deep ponds where they break up temperature stratification. Low pressure air has found many applications in the sewage treatment business and is likely, over time, to find more applications in shrimp farming. High initial costs and the need to remove parts of the system prior to harvest limit the use of low pressure air.
Oxygen injection systems are being used in China and Belize.

Disease:

 Diseases represent the biggest obstacle to the future of shrimp farming. Farms and hatcheries have few defenses against rampaging protozoa, fungi and bacteria, but its viral diseases that pose the greatest threat. They have caused major crashes in Taiwan, China, Indonesia, India, Panama, Honduras and Ecuador. Currently the Western Hemisphere fights a virus that arrived from the east (white spot), and the Eastern Hemisphere fights a virus that arrived from the west (Taura). There are no medications to treat shrimp viruses, but management techniques have evolved which lessen their impact.

In Latin America, prior to the arrival of the white spot virus in 1999, Taura Syndrome Virus was the biggest killer. Shortly after stocking, it can kill from 40 to 90% of the post larvae in a shrimp pond. Although Taura may have been lurking in the background for years, it officially arrived on the shrimp farming scene in June 1992, near Guayaquil, Ecuador. It hit several farms, and then disappeared until March 1993, when it returned as a major epidemic, killing farm-raised shrimp throughout the Gulf of Guayaquil. Dubbed “Taura Syndrome” because it was first reported on farms along the Taura River, an area about 25 kilometers southeast of Guayaquil, it’s also called “Little Red Tail” (La Colita Roja) because the tail fan and body of affected shrimp turn pale pink. Taura has spread to every country in the Western Hemisphere with the exception of Venezuela where hatcheries maintain captive brood stock and restrict the introduction of new brood stock. Belize appears to have eradicated Taura in 1995, only to see it re-appear in 2001. Wild and captive vannamei appear to be developing some resistance to Taura.

In the Eastern Hemisphere, white spot virus rages on, but in places like Thailand, management techniques have brought it under control. White spot usually strikes when the animals have been in the water for more than sixty days, a critical time for the farmer. He’s invested a lot of money in the crop, but the shrimp are usually too small to harvest. In 1996, white spot even attacked extensive farms in West Bengal, India, and the Khulna area of Bangladesh. Now common in both hemispheres, it’s more lethal than Taura, kills many varieties of crustaceans and has many vectors (carriers). Fortunately, white spot is easier to exclude from a farm than Taura because birds and insects don’t appear to be carriers.

Viral attacks in both hemispheres frequently occur after periods of heavy rain, a stressful time for shrimp, when temperatures, salinities and water quality variables fluctuate wildly.

Good water quality and lower stocking densities appear to be the best defense against all diseases. When pathogen populations are low, a shrimp’s defenses are normally capable of preventing disease, but when stressed by questionable water quality and high stocking densities, shrimp fall prey to “shell-loving” bacteria, fungi and viruses.

Hatcheries, which maintain concentrated stocks of live feeds and developing larvae, are particularly susceptible to diseases, which can be introduced with each new batch of wild brood stock, a known source of pathogens.

Bird Predation:

Migrating flocks of birds can land on a shrimp farm and quickly consume most of the shrimp. Almost everywhere birds are protected by law and efforts to scare them away are usually futile. Noise cannons, rockets and scarecrows work for awhile, but the birds soon learn to ignore them.

Pollution and the Environment:

 Whenever large numbers of semi-intensive and intensive shrimp farms concentrate on the same river, estuary or bay, their rich effluents, primarily shrimp waste products, uneaten feed and dead algae and bacteria, lower the quality of the surrounding water, overwhelm the environment and create conditions which favor shrimp pathogens.

Moderate amounts of effluents from shrimp farms have a beneficial effect on the environment, enriching it without overwhelming it. In some cases shrimp farm effluent has improved the local fishery. The mangroves and mangrove species that surround many shrimp farms thrive on moderate amounts of nutrients from shrimp farms. In turn, the mangroves prevent erosion and reduce turbidity by trapping sediments and binding nutrients. Ecuador’s extensive shrimp farms operate in a comfortable balance with the mangroves.

In some parts of Thailand, Indonesia and the Philippines, where pollution has put shrimp farms out of business, mangroves have reclaimed shrimp ponds. In Thailand, Venezuela and Ecuador, shrimp farmers restore and protect mangrove areas.

The Weather:

The weather plays a major role in the shrimp farmer’s life. He never knows what to expect, but must be ready to alter labor, feeding, pumping, aeration and harvesting schedules and then be prepared to operate his business from a boat or plane, while waiting for the restoration of roads, bridges, electricity and communications. Scheduling hatchery and farm operations at these times creates major headaches for the industry. In a very general sense, heavy rainfall and high temperatures benefit shrimp farming.

The El Niño:

 Every three or four years, driven by a reversal in normal wind patterns, an El Niño, a huge bulge of warm water hidden under a blanket of tropical storms, hits the western most extension of South America, burying the cool Humboldt Current and dropping heavy rains on Peru and Ecuador, often around Christmas–hence the name El Niño (the boy), in honor of the Christ Child. Over the past three decades, shrimp farms around the Gulf of Guayaquil, just a few degrees south of the equator, on the Peru/Ecuador border, have learned to deal with El Niño’s various moods and relatives, like his cool weather cousin La Niña.

El Niño is the planet’s most important source of climatic change, causing devastating droughts and storms around the world. The 1991–1993 El Niño (of average intensity, but unusually long) triggered major weather changes and disrupted shrimp farming on a global basis. It caused drier than normal conditions in the Philippines, Indonesia, Thailand, northern Australia, northeastern Brazil and Central America. It brought record drought to southeastern Africa and dropped heavier than normal rains on southern Brazil, Uruguay, central Argentina, California, Texas, Ecuador and Peru. Coastal China experienced unusually heavy rains in 1993.

In 1982–83, a huge El Niño caused droughts and storms blamed for 1,500 deaths and up to $8 billion in damage worldwide. Scientists at Mississippi’s Stennis Space Center think big El Niños like that one influence world weather patterns for over a decade, as they bounce from continent to continent, slowly are dissipating their energy.The granddaddy of all El Niños hit Peru, Colombia and Ecuador in April 1997 and lasted until May 1998.

Production of farm-raised shrimp usually increases along the Pacific coast of South America during El Niño years. Shrimp like the warm El Niño waters and grow rapidly in the brackish-water environment created by the heavy rains, which also flush out the ponds and estuaries. Wild shrimp reproduce in great numbers during El Niños, supplying farmers with endless quantities of the highly-prized wild post larvae. Shrimp hatcheries have a tough time competing with the abundant wild seed stock and most temporarily close their doors.

Although Ecuador’s production of farm-raised shrimp increases during El Niños, big El Niños, like the ones in 1981-82 and 1997-98, result in a net loss to the industry. Roads and bridges get washed out so harvests have to be barged or flown to processing plants. Low-lying ponds get flooded.

In Central America and México, El Niño spawns tropical storms and hurricanes during its early phases, followed by hot, dry weather during its later phases. Shrimp like the warm temperatures, but the absence of rain eventually leads to lower water quality and slower growth, so El Niño is a mixed blessing in this part of the world.

El Niños suppress hurricane formation in the Atlantic Ocean and encourage it along the Pacific Coast of Central America and Mexico. In September 1997 Hurricane Nora, spawned by the 1997-98 El Niño, spun through the Mexican shrimp farming industry and reached as far north as Dr. Donald Lightener’s Shrimp Disease Laboratory at the University of Arizona in Tucson.

In the Eastern Hemisphere, El Niño usually has a negative effect on shrimp production. During the 1991–93 El Niño, major droughts in Thailand, the Philippines and Indonesia took a heavy toll on shrimp farming. Wild brood stock and seed stock were in short supply and disease and water quality problems popped up all over Southeast Asia.

The Monsoon:

The southwest monsoon affects the lives of 60% of the world’s population and has a major controlling effect on world food production. India gets 80% of its annual precipitation from the monsoon, which begins in late May, when southern trade winds in the Indian Ocean push moist ocean air northward toward southwest India. When they hit the coast in June, they warm, rise and shed their moisture. The rising air draws in more cool, moist air, causing heavy rainfall over most of the country.

The monsoon arrives in Trivandrum, Indian, in June and reaches Bangladesh, Thailand, China and the Philippines by the end of summer. In September, when the orbital position of the tilted Earth changes, the wind system reverses, pulling cool, dry air across Asia and carrying rain to Vietnam, Malaysia, Thailand, Southeast India, Sri Lanka, Indonesia and Australia, all of which farm shrimp.

Like El Niño in the Western Hemisphere, the monsoon flushes out rivers and estuaries and has a positive effect on shrimp farming and brood stock supplies. But the monsoon also causes rapidly fluctuating water quality variables that can lead to disease epidemics. And, if the rains flood the ponds, which frequently happens in West Bengal, India and Bangladesh–and elsewhere–its effects can be decidedly negative.

Cyclones, Typhoons, Hurricanes and Tropical Storms: Of the major shrimp farming nations, only Peru, Brazil and Ecuador in the Western Hemisphere and Thailand, Malaysia and Indonesia in the Eastern Hemisphere escape powerful cyclical storms. These storms are called cyclones in India and Bangladesh, typhoons in China and the Philippines and hurricanes in the Western Hemisphere. It’s the huge amounts of rain and the surge of water that precedes these storms that do the most damage, easily flooding out an entire shrimp farming region overnight. The wind also tears buildings and hatcheries apart. These storms hit with enough regularity that shrimp farmers beyond the safe countries should be prepared to deal with at least one every ten years, or so. In addition to the physical punishment, they drop enough water to change the pond chemistry, shocking the shrimp into weakness and often death. Tropical storms lack the punch of the cyclical storms, but they have a similar effect on water quality

Shrimp culture in Bangladesh started to develop in the early 1970s. At that time there was little local demand and the price of shrimp was consequently very low. The potential of farmed shrimp as a hard currency earner was quickly realized by the private sector, and within 10 years more than 26,000 ha of shrimp ponds were under cultivation. During this period the shrimp farming industry received little or no support from the Bangladesh Government. Only since 1980 with the introduction of the Second Five Year Plan (1980–85) has brackish water aquaculture been given official recognition by the Government.

The Directorate of Fisheries has estimated that by the beginning of 1986 more than 115,000 ha had been turned over to shrimp farming activities in the whole of Bangladesh. Shrimp farming takes place in the districts of Satkhira, Khulna, Bagerhat, Barisal, Patuakhali, Bhola, Chittagong and Cox’s Bazar. The two most important areas lie in the Khulna-Satkhira area to the north of the Sundarbans (ca 90,000 ha) and in the vicinity of Cox’s Bazar (ca 24,000 ha). According to the Third Five Year Plan (1985–90) shrimp production is expected to increase from 9,000 t in 1984–85 to 34,000 t by 1989–90.

Market Demand and Economic importance:

The local demand for fish is likely to approach 1.9 million t yr^-1 by the year 2005. Some of this demand will have to be met by increasing the production from existing inland waters through the introduction of improved husbandry and water management practices; however, other sources of fish will need to be sought. Bangladesh has about 2,500,000 ha of coastal tidal lands, of which about 2,167,000 ha may be suitable for aquaculture. There is therefore an enormous potential for increasing fish production through brackish water aquaculture. So far these coastal tidal lands contribute very little to the domestic consumption of fish, although they are already an important and increasing source of foreign exchange through farmed shrimp exports.

The local demand for farmed shrimp in Bangladesh is poor since very few Bangladesh is eating shellfish. However, the international market is extremely important and a major source of hard currency for Bangladesh. It has been projected that the export value of shrimp will have increased from about US$ 57 million in 1984–85 to around US$ 225 million in 1989–90. Most of the shrimp produced in Bangladesh is exported to Japan. Recent export prices for shrimp shipped to Japan are shown in Table 1.

Less emphasis has been placed on the freshwater shrimp market by shrimp processing and exporting companies. This may be a reflection of the preference for marine shrimp in Japan, which is currently the main market for Bangladeshi shrimps. There are increasing market opportunities for both freshwater and brackish water shrimp in Europe, whilst the US market can still absorb additional imports of high quality brackish water species (Rack owe et al, 1983)

Table 1. Shrimp export prices (C & F Tokyo) January 1989.

Most shrimp farms in Bangladesh are operated on a very extensive basis, relying on natural productivity and little or no management. Current production levels generally lie within the range of <50 kg ha^-1 yr^-1 to >300 kg ha^-1, yr^-1, although the majority of shrimp farms are operating towards the lower end of the scale. A few enterprising farmers are claiming production levels of 900 kg ha^-1 yr^-1 or more.

In the long term there is enormous potential to increase the total production of shrimp in Bangladesh. This can be achieved in two ways: first by encouraging the introduction of more intensive shrimp farming methods whereby average production could be increased to >600 kg ha^-1 yr^-1 (Table 2), and secondly by developing freshwater shrimp farming which has the potential of being even more important economically than brackish water shrimp farming.

Much of the area currently used for brackish water shrimp production in the vicinity of Khulna and Satkhira, could be utilized for the production of both brackish water shrimp during the dry season and freshwater shrimp during the rainy season. The latest estimate (1986) of the area of land under shrimp production is 115,000 ha, this leaves an enormous potential for increasing not only brackish water and freshwater shrimp production for export, but also brackish water fish production for local consumption.

SHRIMP FARMING INDUSTRY IN BANGLADESH:

Since arriving in Bangladesh, field visits have been made to the two main shrimp growing areas: the region south of Khulna and Satkhira, and the peninsula from Cox’s Bazar to Teknaf. The Khulna-Satkhira region was visited from the 17th to the 21st April 1988. Whilst in the area, the site of the proposed Brackishwater Station (BS) at Paikgacha was visited on the 18th April with the appointed CSO, Dr Aminullah Bhuiyan. The Cox’s Bazar-Teknaf coastal area was visited from the 24th to the 30th April 1988. A summary of the various field trips appears in APPENDIX D.

The following synopsis of the present status of the shrimp farming industry in Bangladesh has been based to a large extent on the excellent sectoral review prepared by Karim (1987) together with personal observations made during the field visits during the first part of the assignment in 1988.

Fisheries production in Bangladesh is extremely important to the economy. Although the capture and culture fisheries contribute about 2.9 % of the GDP and 9 % of foreign exchange earnings, fisheries products account for 6 % of the total per capita protein intake and about 80 % of the per capita animal protein intake. The estimated total fisheries production in Bangladesh during 1983–84 was 751,000 t. The production from inland waters was about 577,000 t (77 %), of which 118,400 (21 %) was contributed by aquaculture. In recent year’s fisheries production has declined from about 822,000 t in 1974– 75, whilst daily per capita fish consumption has fallen from 33 g in 1963–64 to 21 g in 1983–84 (a decrease of 36 %).

Even if per capita fish consumption is to be maintained at the current level, fisheries production will need to be increased to 1,100,000 t by the year 2005 in order to keep pace with the projected population growth. If daily per capita fish consumption is to reach 38 g (recommended by the Institute of Nutrition and Food Science) then production will have to be increased to 1,900,000 t. This represents an increase of about 150 % above present fisheries production levels. The Government of Bangladesh has therefore introduced an ambitious fisheries development programme in the Third Five Year Plan (Anon, 1985a), to increase production from both inland and saline waters for both domestic consumption and for export (Rahman, 1986; Anon, 1985b).

At the present time brackish water aquaculture is virtually limited to shrimps of the genera Macrobrachium and Penaeus. Penaeid shrimps (mostly Penaeus monodon) currently provide an increasing source of foreign currency through exports to the USA, Europe and particularly Japan. Brackishwater aquaculture production for local consumption is minimal. Smaller, commerically less important penaeid shrimps (Metapenaeus brevicornis and Metapenaeus Monoceros) and some Macro brachium Rosenberger are consumed locally. Small quantities of mullet (Mugil spp) are also produced as a by-product or secondary crop in some shrimp ponds.

Shrimp culture in Bangladesh started to develop in the early 1970s. At that time there was little local demand and the price of shrimp was consequently very low. The potential of farmed shrimp as a hard currency earner was quickly realized by the private sector, and within 10 years more than 26,000 ha of shrimp ponds were under cultivation. During this period the shrimp farming industry received little or no support from the Bangladesh Government. Only since 1980 with the introduction of the Second Five Year Plan (1980–85) has brackishwater aquaculture been given official recognition by the Government.

The Directorate of Fisheries has estimated that by the beginning of 1986 more than 115,000 ha had been turned over to shrimp farming activities in the whole of Bangladesh. Shrimp farming takes place in the districts of Satkhira, Khulna, Bagerhat, Barisal, Patuakhali, Bhola, Chittagong and Cox’s Bazar. The two most important areas lie to the north of the Sunderbans (ca 90,000 ha) and in the vicinity of Cox’s Bazar (ca 24,000 ha).

Most shrimp farming has developed within polders created by the Bangladesh Water Development Board (BWDB) in low-lying coastal flood plains. Often these activities have been started without the consent of the BWDB, and one of the major concerns has been the creation of unauthorised sluice gates or channels through the perimeter dykes of the polders. Only those areas that are low enough to permit inundation of the land by at least 0.5 m of water at spring tides have generally been used for shrimp farming.

Only two species are deliberately stocked in ponds: P monodon and M rosenbergii. Of these P monodon is by far the more important. Other species of penaeid shrimps are also cultivated, through the accidental introduction of their fry when the ponds are filled or water exchange takes place. These include: Penaeus indicus, Penaeus merguiensis, and M Monoceros and M brevicornis.

Shrimp farming in Bangladesh relies entirely on the supply of wild fry for stocking purposes. It has been estimated that 1–3 billion fry of P monodon were harvested in 1985. The main collection centres are Satkhira, Khulna, Bagerhat and Cox’s Bazar. At present, most fry collection for P monodon is conducted within the rivers and creeks of the coastal flood plain. It has been suggested that there may be a huge unexploited resource within the Sundarbans.

Collection of shrimp fry is carried out using either a fixed bagnet which relies on tidal streams in small rivers and creeks to carry post larval shrimp into the codend, or alternatively triangular (or less frequently rectangular) nets which are pushed or pulled along the bed of the river or creek. In Cox’s Bazar shrimp fry collection is also carried out along the beach. In the Khulna-Satkhira area the peak season for shrimp fry is February-May, whilst at Cox’s Bazar it is April-June.

Shrimp fry collectors transfer their catches to earthenware bowls which are then carried back to the villages where the fry are sorted and counted by children using white enameled plates. This undoubtedly results in a very large wastage of fry of both penaeid shrimps and other commercially important species including fish. The shrimp fry then pass through a chain of middlemen before reaching the shrimp farmers, during which the fry are usually transported in 20–30 l aluminum vessels using every conceivable form of transport.

Shrimp fry mortality is believed to be very high, due to extreme water temperature and salinity fluctuations, low dissolved oxygen levels, and even the use of table salt used in the mistaken belief that it will provide the right salinity for the fry.

The price of P monodon fry in the Khulna-Satkhira area has risen dramatically from about Tk 40–50 in 1980 to Tk 400–600 per thousand (postlarvae of ca 15 mm total length) in 1988. The price of shrimp fry is much lower in the vicinity of Cox’s Bazar being only Tk 40–100 per thousand for fry of a similar size.

Macrobrachium fry (postlarvae and juveniles) are collected in the Khulna region for stocking freshwater or low salinity brackish water shrimp farms. There are no estimates available of the number of fry collected annually. Fry are available in the Khulna area from April onwards with the peak demand occurring in July. The price of Macrobrachium fry in the Satkhira area in 1986 was Tk 500–1,000 per thousand (25–50 mm total length), although at Paikgacha prices were only half this figure. Hatchery reared Macrobrachium fry produced in Cox’s Bazar were being sold in 1988 for Tk 440 per thousand (15–20 mm total length).

In the Khulna-Satkhira area the shrimp farming pattern, often in rotation with agriculture, reflects the ambient seasonal salinity fluctuations in response to the monsoon:

January-July [high salinity season]:

• Culture of brackish water shrimp and fish.
• Harvesting of marketable individuals.

August-December [low salinity season]:

• Continued culture of under-sized shrimp and fish subject to the salinity tolerance of the species in low-lying areas.
• Culture of freshwater shrimp and fish.
• Cultivation of slightly salt-resistant aman rice in more elevated areas.
• Harvest of residual brackish water shrimp and freshwater shrimp.

In the Cox’s Bazar area this pattern may be reversed due to the generally higher ambient salinities. Therefore some farmers produce salt during the the dry season and brackish water shrimp during the rainy season.

Most of the shrimp farming is carried out within large dyked areas (polders or ghers). Transplanted aman rice can be grown from August-December, when water and soil salinities are low. Agricultural crop production from January to July is difficult due to the shortage of freshwater and increased salinities in the soil. Acid sulphate soils may also present special problems in some areas.

Before the recent and rapid growth of shrimp farming, the land used to be left fallow during the dry season and used instead for grazing cattle and water buffalo. Animal dung remaining on the land, if not collected for fuel, would help to increase the production of aman rice in the following rainy season. The loss of grazing has resulted in very serious conflicts in land use in some areas.

Until recently all shrimp farmers, either individually or in groups, has leased land within BWDB polders. In some cases the land has been re-leased from the rightful leaseholders by force. The BWDB perimeter dykes are deliberately breached and wooden sluice gates or reinforced concrete culverts installed before repairing the dykes. The ponds which may extend up to 500 acres (200 ha) or more are usually allowed to remain dry during January after harvesting the rice. The stubble is left in place. The ponds are then flooded during spring tides.

Since the early 1980s the Government of Bangladesh has played an active role in improving the level of shrimp farming husbandry and technology. Screens to prevent the entry of predators and competitors have become much more widespread, in combination with the selective stocking of fry. Simple nursery productions methods have been introduced in some cases through the construction of a shallow nursery pond within the confines of each grow out pond. Pond preparation, liming, fertilization, pest control, nursery production, supplementary feeding and water management have only started to be introduced during the last five years, and even now are employed in only a few areas.

Recently P monodon production has been increased by the more enterprising farmers from <50 kg ha^-1 yr^-1 to >300 kg ha^-1 yr^-1. In the case of the Allah-Wala shrimp farm at Cox’s Bazar (see APPENDIX D) a production of up to 900 kg ha^-1 yr^-1 was claimed during 1988.

There are plenty of signs that shrimp production levels in Bangladesh will continue to rise as a result of the gradual introduction of more intensive practices. At the present time, however, most farms are operated on an extensive basis, with relatively few examples of semi-intensive production.