♦ Description and ecological character

  • Morphological feature: Rostrum is long and has 6-9 teeth on dorsal margin and 3-6 teeth on ventral margin of rostrum. Thelycum of female is the closed type. Body is pale grey in color and has number of minute spots on entire surface.

  • Ecological character: This species occurs from the coast of north China and the west coast of Korea. The species spends in the southern coast of Korean sea for overwintering period and migrates up along the southern and the western coasts in April to June. The species spawn in river mouths and shallow waters from May to June. Spawned larvae grow in shallow waters and begin to migrate into the southern area from November when water temperature drops below 10℃. Fishermen collect only the females using fishing boat with bottom gill-net during spring tides from late April because the species mates in winter period and the female keeps spermatophore on thelycum until spawning occurs in next spring. The species better maturate in lower water temperature (10-14℃) than other farmed shrimp species and readily spawn in indoor tanks without eyestalk ablation or regulation of photoperiod.
 

♦ Status of shrimp farming in Korea

Shrimp farming was initially begun in 1960s in Korea and the farming industry was developed in 1980s. Farmed shrimp production has been rapidly increased since 1990s. Farmed shrimp production reached 3,256 MT in 2001. Number of shrimp farms is about 450 and total farmed area is about 2,600 ha. More than 90% of shrimp farms locate in the western coast and the rest is along the southern coast.

Two species, Fenneropenaeuschinensis (Chinese fleshy prawn) and Marsupenaeus japonicus (Japanese Kuruma shrimp) had been cultured before the middle of 1990s, but M. japonicus had not been cultured after outbreak of WSSV (white spot syndrome virus) in 1993.

Pacific white shrimp (Litopenaeus vannamei) was firstly introduced from USA in 2003. NFRDI imported three hundreds of SPF (specific pathogen free) broodstock from Hawaii, succeeded production of post-larvae and grew up to 20g in body weight in indoor tanks. For commercial purpose some shrimp hatcheries began to import SPF broodstock from USA in 2004 and the potential of white shrimp farming is expected to increase in next few years.

 
Table 1. The number of shrimp farms and farmed area in Korea.

Table 2. The number of stocked postlarvae to outdoor ponds and final mortality rate in Korea.

♦ Aquaculture technique

 • Pond culture
All shrimp farms consist of earthen ponds using well-developed mud flats along the western coast. Size of pond is 1-3 ha and shape is square. Pond consists of inlet and pumping system, water supply canal, reservoir (1/3 of pond size) and drainage canal. Pond construction begins in February to March. First, farmers remove sludge of bottom and reconstruct dikes using tractor. Water is filled after construction and chlorinated with calcium hypochloride with 10-20 ppm in final concentration in order to kill pathogens including viral vectors and others. After sterilization of water, lime is treated. Water is maintained from 1.2 to 1.5m in depth.
 

 • Larval production

 The number of shrimp hatcheries is more than 15 in Korea. Annual production of postlarvae is about 800-900 millions/year. Shrimp larvae are produced once a year (May to June) because of Korean climate. Larval production completely depends on wild broodstocks. Fleshy prawn spends the winter season in the southern coast of Korean sea and migrates up along the western and the southern coasts in April to June. Spawning season of this species is May to June. Farmers collect only females for spawning because the females had already mated in the last winter season. The collected females are maintained in 50-100 MT circular FRP tanks at 16-18℃ in hatcheries. Stocking density of females is 1-2 inds. /m2, but farmers usually stock up to 3 inds. /m2. A female carries 300 thousands to 1.1 million eggs and 80-90% of them are spawned.
   When the ovary of female is not fully developed, the females are maintained at 12℃ and fed with squid mantle, clams and bloodworms to induce maturation. The fleshy prawn is not sensitive to light and regulation of photoperiod is not necessary. Optimal temperature of this species is 10-12℃ and higher temperature than 14℃ will inhibit ovarian maturation. When the females are fully matured, water temperature is raised up to 16-18℃ to induce spawning. Spawning always occurs at night. Spawned females are moved into another tank filled with filtered seawater to induce the second spawning. A female can spawn three times at most and then discarded.
   Eggs are hatched into nauplii in 35 hrs at 19℃ after spawning. Hatching rate is about 80-90%. Hatched nauplius larvae pass through 6 nauplius stages, three zoeal stages and three mysis stages and metamorphose to post-larva in three weeks. During the nauplius stages, food is not provided. Zoeal stages are fed with microalgae including Skeletonema costatum, Chaetoceros sp. and Nizschia sp. To maintain microalgae in good conditions, organic nutrients are sometimes provided. When the larvae molt to zoeae, rotifers and artificial larval feed are provided. For the mysis stages, Artemia nauplii are provided. Daily feed amount is about 200% of larval biomass. When larvae grow up to 2cm in body length, they can be used for stocking in outdoor ponds.

 • Stocking of larvae
  Post-larvae are packed in plastic vinyl bags saturated with pure oxygen or moved to outdoor ponds by vehicles equipped with water tank and aerator. Age of larvae for stocking is PL8-PL12, stocking density is 25-35 PL/m2, and stocking time is May to Jun when water temperature raises up to 18℃.
 
 • Growout and harvest
  Period of growout is 120 to 150 days in outdoor ponds. Shrimp are fed with artificial pelletsduring entire growing period. Protein requirement of fleshy prawn is higher than Pacific white shrimp (protein content of feed is 40-45%). Feeding frequency is three to six times daily according to shrimp age or farmers. When farmers provide feeds, small motor boats are used in big ponds and farmers spread out feeds by hand in small ponds. FCR (feed conversion ratio) is about 1.5-2.0.  
  Management of rearing water is the most important during growing period. To maintain alkalinity and pH in optimal condition, lime is sometimes provided to ponds. To increase DO concentration, paddle wheel aerators are installed in 8-10 HP/ha and provided with liquid oxygen in emergency. Because the fleshy prawn has a migration habit, water flow should be maintained using paddle wheel aerators.
  Harvest begins from late August and finishes in October. Because the shrimp will not eat feeds when water temperature falls below 15℃, harvest should be completed before the middle of November. Farmers use long line nets with pockets to collect shrimp. Shrimps swim one way and are trapped into pocket of net. Most of collected shrimps are transported with truck equipped with water tank and consumed alive. The price of live shrimps on farm is 15-20 US$ (40-50 pcs. /kg).

Mature females for spawning. Larval production depends on wild broodstock in Korea.	Indoor tanks for larval rearing in hatchery. About 15 hatcheries produce 800-900 millions larvae a year.	Microalgae culture for larval rearing.
Farmer is harvesting postlarvae from larval rearing tank in a hatchery.	Farmer is stocking postlarvae into growout pond.	Typical earthen ponds. Outdoor pond is about 1-3 ha in size, rectangular in shape and equipped with paddle wheel aerators for increasing DO.
A farmer is preparing feeds in his boat. (Right) A farmer is providing feeds to shrimp.	A farmer is providing feeds to shrimp.	Liquid oxygen is prepared in most shrimp farms for emergency.
A farmer is monitoring feed tray after feeding.	Harvesting net. Long net with pocket at the end is used for collecting shrimps.	Customers are enjoying roasted shrimps in a local restaurant. Farmers provide live shrimp to restaurants.
A greenhouse with RAS(recirculation aquaculture system) for F. chinensis culture. About 3.2kg/m3 of F. chinensis (mean body weight 21g) is produced in this farm.	Indoor tanks of 270m3 in volume inside greenhouse RAS farm.	A juvenile shrimp for releasing is marked with fluorescent dye (red color in the 6th abdominal segment).
Juvenile or nursery-cultured postlarvae are released into the sea to increase shrimp resources.

 • Diseases
  Parasitic, bacterial and viral diseases cause serious economic damage in shrimp farms every year. The most frequent parasitic disease is a ciliate, Zoothamnium sp. which is found on shrimp gills in July to August.
  Major bacterial diseases are caused by Vibrio parahaemolyticus, V. harveyi, V. spp., and Aeromonas spp., and occur in
July to September. Three kinds of viral diseases, HPV (Hepatopancreatic Parvo-like Virus), BMN (Baculoviral Midgut Gland Necrosis Virus) and WSSV are found in Korean shrimp ponds. HPV was reported from F. chinensis in 1991 and BMN was reported from M. japonicus in 1991. WSSV was first reported from M. japonicus in 1993. Among them, WSSV causes the biggest economic losses to shrimp industry in Korea. WSSV is not only present in shrimp but also occurs in other crustaceans including various species of crabs and shrimps. In cultured shrimp, WSSV infection can reach a cumulative mortality of up to 100% within 3-7 days and has caused the most serious damage in the shrimp farming industry.