WHITE SHRIMP Litopenaeus vannamei PRODUCTION IN FLOATING CAGES AT SEA AND POLYCULTURE WITH PACIFIC OYSTER Crassostrea gigas  

Ricardo Radulovich* and José Pablo Fuentes
 
Department of Agricultural Engineering
University of Costa Rica, San José, Costa Rica
ricardo.radulovich@ucr.ac.cr
 

White shrimp (Litopenaeus vannamei) was farmed at small scale, alone and with Pacific oyster (Crassostrea gigas), in low-cost floating cages at sea near-shore in the Gulf of Nicoya, Pacific coast of Costa Rica, by men and women of fishing communities. Growth and farming data were collected for 19 separate production events in six localities, seven of them including full oyster cycles. Shrimp post-larvae (PL12) were placed in a sequence of two or three cages in densities leading to a mean at harvest of 4.05 kg m-3 (SD = 1.16 kg m-3) of 12 g shrimp after 121 days with 59.7 % mean survival. Growth rate between 1.0 and 18.0 g was 1.1 g week-1, decreasing to 0.65 g week-1 through 35.4 g. Oyster seed were grown within shrimp cages in simple lanterns, at a harvest density of 100 70-mm oysters m-2 of cage after 5.4 months growth, with 46.8 % mean survival. Shrimp PL were fed powdered concentrate feed until 0.1 g when they were weaned into a diet of only 'trash' fish and fish byproducts aiming at 8 g fresh feed: 1 g of shrimp growth, with no significant differences in weight gain compared to a diet of 2 g concentrate feed: 1 g of shrimp growth (paired t-test; p < 0.05). A mean fresh-feed conversion rate of 6.45 was obtained by growers. While several biological benefits of polyculture were evidenced, no significant differences on growth of shrimp were determined; however, financial impact was substantial. Besides selling shrimp for live bait, profit markedly increased when adding oyster in polyculture and using fresh instead of concentrate feed. The latter also promoted a closer integration with fisheries and decreases organic pollution from using concentrate feed. Also, cages with shrimp functioned as fish-attracting devices. Seaweed cultivation on the water surface and sea cucumbers in the bottom of cages established a highly diversified and intensive multi-niche polyculture, possible in cages because water is fully exchanged constantly. Overall, little training was needed to successfully implement the innovation although care during early growth was often inadequate. Fishing moratoria, theft and vandalism inhibited outspreading, evidencing the need for institutional support and proper policies.