Lecture 9 crustaceans 2 shrimp and prawn

Editor's Notes

• #3: Total world harvest from aquaculture and wild capture was 3.2 million metric tons in 1999. About 768 million metric tons, 24% of the total world harvest, of marine shrimp was farmed. The U. S. is the fourth leading producer of wild captured marine shrimp after China, India and Indonesia. However, the farmed harvest of marine shrimp in the U. S. is about 2,100 metric tons, less than 0.02% of world farmed harvest. Marine shrimp are the most popular seafood among U. S. consumers. Thailand is the leading producer of farmed marine shrimp.
• #52: Marine shrimp are farmed in most countries with a tropical climate and access to the sea. The two most popular cultured marine shrimps are Pacific white shrimp, Peneaus vannamei, and the Pacific tiger shrimp, Peneaus monodon.
• #53: The Pacific white shrimp is native to the west coast of Mexico, Central America and Colombia, Ecuador and Northern Peru. The Pacific white shrimp has been introduced into the southern U. S., the east coast of Mexico, Central America and the Caribbean and Atlantic ocean coast from Colombia to Northeast Brazil. Some Caribbean Islands have also introduced the Pacific white shrimp. The Pacific tiger shrimp is native to the warm tropical waters of the western Pacific and Indian oceans.
• #54: The Pacific white shrimp is preferred for culture in the Western Hemisphere. The white shrimp is benthic, feeding on worms and microorganisms attached to detritus found on the bottom. Preferred water temperature and salinity ranges between 25 and 30o C and 15 to 25 ppt, respectively. However, the Pacific white shrimp can be culture in low salinities and freshwater with high alkalinity, hardness and cloride ion content. In the U. S., the white shrimp can be raised in open ponds only in the summer when water temperatures permit good growth. Shrimp that are not maintained indoors in warm water will died during the winter months in open ponds. The Pacific white shrimp reaches sexual maturity in 1 year.
• #55: Adults spawn in the open ocean. Thes eggs and larvae are carried by currents into the esturaries where the young shrimp feed and grow among the mangrove forests. As the shrimp mature at 1 year of age, they swim back to the open ocean to spawn.
• #56: Marine shrimp are harvested from coastal waters by trawl nets pulled by boats. Marine shrimp captured from the ocean have been processed and marketed in the U. S. for many years. Marine shrimp is the most valueable seafood sold in the U. S. Marine shrimp farming blossomed in the past 20 years. Shrimp farmers took advantage of the processing facilities and marketing network established by the marine shrimp capture industry to export their shrimp to the U. S., Europe and Japan.
• #57: Small shrimp ( postlarvae ) for stocking ponds can be captured from the wild. Small mesh push nets are used in the shallow estuaries to capture postlarvae. Postlarvae captured in the wild often have both desireable and undesireable shrimp species along with small predacious fishes. Separation of desireable shrimp postlarvae from undesireable shrimp postlarvae is difficult and usually all postlarvae are stocked.
• #58: Postlarvae can also be produced in captivity. Numerous larval stages are passed before reaching the postlarval stage. Natural food ( phytoplankton ) must be provided to the larval stages grown in the hatchery. However, only desireable shrimp species are raised and contamination with undesireable organisms is not a problem.
• #59: Mature females can be captured ( carrying sperm packet ?) from the ocean and transported to the hatchery or the males and females can be matured in captivity. Capturing mature females from the ocean is cheaper than raising brood shrimp in cativity. However, disease transfer and genetic improvement is more easily controlled when brood shrimp are raised in captivity.
• #60: Postlarvae are stocked into earthen ponds for growout to market size.
• #61: Ponds are normally constructed on salt flats that have little vegetation and are flooded at high tide twice a month. Ponds can also be built on dry land next to estuaries that is never flood at high tide. Some shrimp ponds have been built in mangrove forest. However, building ponds in mangrove forest is more costly than building pond on salt flats or dry land. Also, mangrove forests are important nursery areas for many young marine organisms and should be preserved.
• #62: Shrimp ponds are large, 5 to 10 hectares in area, and should have flat bottoms without obstructions to assist with pond draining and shrimp harvest. Water depth averages 1 m.
• #63: Salt water is pumped from estuaries into earthen distribution canals. Water flows from the distribution canals into the ponds. Large amounts of water are normally required to farm shrimp. Large diesel fueled pumps are use to lift water into the distribution canals. Some shrimp farms can use tidal water to fill ponds. However, most farms only have access to tidal water a few days per month so pumps are needed to assure water supply on demand.
• #64: Concrete structures called “ monks” or gates control the entrance, exit and depth of water in the ponds. Screens are used to filter the water as it enters the ponds to remove unwanted aquatic organisms and to stop the shrimp from leaving the ponds with water outflow.
• #65: Shrimp are grown to markets using extensive, semi-intensive and intensive systems.
• #66: Initial efoorts to farm shrimp used extensive culture methods. Often, shrimp are allowed to enter the pond with the tide. No control over the quantity and species of shrimp that enters the pond is maintained. Sometimes the pond entrance is screened to reduce unwanted shrimp and predators from entering the pond with tidal water. The number and species of shrimp desired is stocked into the pond. Stocking density is low, less than 4 shrimp/m2. Spond water is not fertilized and shrimp are not fed. Shrimp growth and yield are dependant on natural water fertility and the food organisms produced in the pond. Shrimp yield per area is low, ( ? ), but cost of production is also low.
• #67: Water entering ponds managed semi-intensively is contolled and filtered. Stocking density is between 15 and 25 postlarvae/m2 of pond. Pond waters are often fertilized with organic or inorganic fertilizers to increase fertility. Shrimp are fed daily but naturally produced food organizms are important for fast shrimp growth and high yields. Some pond water is exchanged daily to assure that good water quality is maintained. Ponds that have little or no water exchange are aerated mechanically to maintain high levels of dissolved oxygen.
• #68: Shrimp are fed sinking pellets evenly distributed over the pond water surface. Shrimp are benthic feeders and will not rise to the water surface to eat floating pellets. Shrimp are unable to consume a whole pellet but slowly nibble the pellet, consuming small particles. Feed can be placed on trays to help determine shrimp appetite. Trays are checked 1 to 2 hours after feeding to see if the daily allotment of feed is consumed by the shrimp. If feed is not consumed, the daily allotment is is reduced.
• #69: Small circular and retangular earthen ponds and contrete tanks are used to culture shrimp intensively. Ponds are stocked with 35 to 250 shrimp/m2 and pond water exchange and mechanical aeration is provided continually. Shrimp are fed nutritionally complete pelleted feeds and natural pond foods are not important for fast growth and high yields.
• #70: Cast nets are used to capture shrimp and check for growth rate weekly. Shrimp that are not growing well must be fed more or pond water exchange increased to improve water quality.
• #71: Intensive shrimp culture has expanded rapidly in some regions. Demand to fill ponds and exchange pond waters has increased. Effluents are released back into water supply canals or estuaries. Water quality deteriorates and shrimp mortality increases due to diseases.
• #72: In some cases, the shrimp farming industry collapses because of high shrimp mortality during growout.