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About Shrimp Farming

Factors Affecting Production
The Weather

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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 growout ponds. With the one-phase cycle, the nursery ponds
are eliminated, and the shrimp are stocked directly into growout 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.



Hatcheries sell two products: nauplii (tiny, newly hatched, first stage larvae) and postlarvae (which have passed through three larval stages). Nauplii are sold to specialized hatcheries which grow them to the postlarval 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 postlarvae. Postlarvae look like adult shrimp and feed on zooplankton, detritus and commercial feeds.

Farmers refer to postlarvae 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 postlarvae 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, postlarvae, 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 postlarvae due to its closer approximation of natural conditions and the absents of therapeutics. Survival, from stocking to harvested postlarvae, is usually 40%, or less.

Large-Scale Hatcheries: These are multimillion-dollar, high-tech facilities that produce large quantities of seedstock 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 seedstock 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 broodstock 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, email

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 postlarvae, which are sold to farms for stocking in nursery or growout 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) seedstock 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.


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

Farmers stock postlarvae 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 postlarvae; and decrease feed waste. Because low salinity levels can be lethal to postlarvae, nurseries also provide a halfway house where salinities can be adjusted to pond levels.

The main criticism of nursery systems is that postlarvae suffer mortalities when they are transfered to growout 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 growout 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 growout 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 growout 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 postlarvae for about 28 days and then move them to growout 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 whitespot. They produce large (a little less than two grams), whitespot-free, stress-free juveniles--which doesn't mean they won't get whitespot, 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, webpage

Acclimation Tanks: In the Western Hemisphere, acclimation tanks, pond-side facilities for receiving and conditioning postlarvae, are being replaced by nurseries, which produce larger postlarvae for stocking.

But acclimation have some advantages: Since they're on top of the pond banks, or higher, it's easy to transfer seedstock to ponds. They make it easy to observe and evaluate incoming seedstock, 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 seedstock 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 postlarvae per liter, depending on animal size and duration of acclimation.


Once a growout operation is stocked with postlarval 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.

Growout operations come in all shapes and sizes. They are classified by stocking densities (the number of seedstock 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 postlarvae and sell them to extensive farmers for stocking. Overall, however, stocking densities are quite low, not over 25,000 postlarvae 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 postlarvae per hectare, there is more competition for the natural food in the pond, so farmers augment production with shrimp feeds. Wild or hatchery-produced postlarvae are stocked in growout 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 postlarvae 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 flocs to develop in their super-intensive ponds. The flocs remove nitrogenous waste products from the water, and the shrimp feed on the flocs! 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 cost 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 whitespot, 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 postlarvae 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, email, webpage

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 it's 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 (whitespot), 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 whitespot virus in 1999, Taura Syndrome Virus was the biggest killer. Shortly after stocking, it can kill from 40 to 90% of the postlarvae 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 broodstock and restrict the introduction of new broodstock. 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, whitespot virus rages on, but in places like Thailand, management techniques have brought it under control. Whitespot 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, whitespot 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, whitespot 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 broodstock, 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 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 postlarvae. Shrimp hatcheries have a tough time competing with the abundant wild seedstock 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 Lightner'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 broodstock and seedstock 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 broodstock supplies. But the monsoon also causes rapidly flucutating 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.

Source: 2. Bob Rosenberry, Shrimp News International, October 31, 1988.

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