Shrimp (Litopenaeus vannamei) artisanal production in floating cages at sea and polyculture with oyster (Crassostrea gigas)

Abstract

To complement dwindling fisheries, white shrimp (Litopenaeus vannamei) was cultured at small scale by men and women of six fishing communities in low-cost floating cages made by them at sea near-shore in the Gulf of Nicoya, Pacific coast of Costa Rica. Growth and farming data were collected for 19 separate production events, six of them including polyculture with Pacific oyster (Crassostrea gigas). Shrimp post-larvae (PL) were placed in a sequence of two or three cages in densities leading to a mean at harvest of 4.05 ± 1.16 kg m−3 of 12 g shrimp after 121 days with 59.7 ± 6.4% mean survival. Growth rate between 1.0 and 18.0 g was 1.1 g wk−1, decreasing to 0.65 g wk−1 through 35.4 g. Oysters were grown within shrimp cages in suspended socks or in simple lanterns, at a harvest density aiming at 100 70-mm oysters m−2 of cage after 5.4 ± 0.7 months of growth, with 46.8 ± 18.7% mean survival. No significant differences in growth of shrimp in monoculture between localities or in polyculture with oyster were determined. Shrimp PL were fed powdered concentrate feed until 0.1 g when they were changed into a diet of only fish discards and fish byproducts aiming at 8 g fresh feed: 1 g of shrimp growth. This feeding rate showed no significant differences in weight gain compared to a diet aiming at 2 g concentrate feed: 1 g of shrimp growth as determined in two closely-monitored separate trials. A mean fresh-feed conversion rate (FCR) of 6.0 ± 0.4 was obtained though growers used an overall fresh-FCR of 6.46 ± 1.13. Estimated financial profitability increased markedly when selling shrimp for live bait, adding oyster in polyculture and using fresh instead of concentrate feed. The latter also promoted a closer integration with fisheries as well as a use of fish and byproducts that otherwise are discarded to sea. Overall, 2.5 d of training of participants plus follow-up by project personnel were adequate for them to successfully implement the innovation, although care during early growth was sometimes faulty. Fishing moratoria, dysfunctional social organization, and theft and vandalism inhibited scaling-up, evidencing the need for institutional support and proper policies for widespread adoption.