CRUSTACEAN CULTURE 



CORNELIUS R. MOCk' 



SHRIMP, PENAEUS JAPONICUS 



One of the most valuable marine species in Japan 

 is the "kuruma-ebi," Penaeiis japonicus, shrimp 

 fishery, which commands a price of 7-30 U.S. doUaFS 

 per kilogram, at the Tokyo Central Fish Market. 

 Although this price is high compared to U.S. prices, 

 it is due to the fact that the Japanese people demand 

 live shrimp for the preparation of a delicacy known 

 as tempura. 



Over the years much time has been spent develop- 

 ing methods of holding this species in ponds and 

 rearing it to market size. Even though the Japanese 

 have successfully reared shrimp through several 

 generations, they explained that it was not economi- 

 cal to rear shrimp to sexual maturity because it was 

 time consuming and because the fecundity of the 

 females was reduced. Therefore, gravid females are 

 purchased directly from the commercial fishing 

 fleets and then spawned. 



Once the eggs have hatched, the water is fertilized 

 to stimulate the growth of diatoms. Predetermined 

 amounts of fertilizer and seawater are added each 

 day to the tank until the larval shrimp have reached 

 the last mysis stage. Brine shrimp nauplii {Artemia 

 spp.) are fed from the last mysis stage through the 

 fourth postlarval stage. The shrimp are then fed 

 fresh meats of clams ( Venerupis philippinanini) and 

 mussels (Mytilus ediiUs), which are crushed and dis- 

 tributed throughout the ponds. Because it is too 

 costly and time consuming to separate the crushed 

 shell from the meats, the shell eventually covers the 

 pond bottom, resulting in a substrate that hampers 

 the burrowing of the shrimps. Thus, ponds must be 

 drained or dredged periodically to remove the shell 

 debris. 



.Although larval rearing techniques are primarily 

 the same today as the> were 10 yr ago. research in 



' Contribution No. .'4.' from the National Marine Fish- 

 eries Service. Biological Laboratory. Galveston. Texas. 



- Gulf Coastal Fisheries Center. National Marine Fisheries 

 Service. NO.'X.A. Fon Crockett. Galveston. TX 77.s.sO. 



shrimp culture has been expanded due to three im- 

 portant factors: 1) the rising demand and costs for 

 fresh food items to be fed to the shrimp: 2) the rising 

 wages of employees; and 3) disease problems en- 

 countered. 



Of particular interest is the use of a by-product of 

 soy sauce production, a cake which is ground into 

 powder to fertilize the water. Not only does it stimu- 

 late the growth of diatoms, but the larval shrimp also 

 eat it. As the shrimp grow in size, this powder is 

 either extruded or pressed into a size suitable for 

 eating. At the Kagoshima Prefecture Fisheries Ex- 

 perimental Station, the Director, K. Shigeno, re- 

 marked that although the shrimp ate this artificial 

 food and grew to market size, the consumer was not 

 satisfied with the quality or color of the prawns. He 

 felt that the problem was primarily a vitamin defi- 

 ciency. Artificial foods with a variety of additives 

 are being tested at Shigeno's laboratory. 



Research is also being directed toward rearing 

 prawns to market size in a closed system. A 1,000-m^ 

 cement tank (23 m in diameter and 3 m deep) has 

 been built at the Tarumizu Kagoshima Prefecture 

 Fish Experimental Station. The water temperature 

 can be controlled, and a false bottom with airlift 

 pipes has been installed as an in-bottom filter. 

 Twenty-day-old postlarval shrimp have been 

 stocked in this tank and reared to market size with 

 good results. However, during two recent experi- 

 ments a number of problems occurred, resulting in 

 poor production. 



Circulation of the water mass within a rearing 

 system was emphasized for either fish or shrimp 

 culture. At Tarumizu Kagoshima Prefecture Fish 

 Experimental Station the flow was maintained with 

 water jets, while a large mechanical stirrer was being 

 tested at Setonaikai Saibai Gyogyo Center. Tamano 

 Jigyojo. 



At the Nansei Regional Fisheries Research 

 Laboratory. H. Kurata spoke about the natural 

 waves of P. Ja[>(>iii(ii.s postlarvae that enter the es- 

 tuaries. Monitoring of these waves now indicates 



111 



