Aquaculture Crsp 21st Annual Technical Report

The survey on tilapia-shrimp polyculture was conducted in Thailand and Vietnam from March through June 2002. The survey conducted in Thailand was to assess the current status of farmers’ practice of tilapia-shrimp polyculture, while the survey conducted in Vietnam was to find out why Vietnamese shrimp farmers do not grow tilapia in shrimp ponds. In twelve provinces of Thailand, 61 farmers who culture fish in their shrimp farms were selected and interviewed using a structured checklist and open-ended type of questionnaires. In the Mekong Delta of Vietnam, university researchers, local shrimp farmers association and local government fisheries staff, and shrimp farmers were interviewed. Results showed that three versions of tilapia-shrimp polyculture—namely simultaneous, sequential, and crop rotation systems—are practiced by Thai shrimp farmers. Among all interviewed farmers, 42.6% use a simultaneous polyculture system, while percentages of farmers using sequential and crop rotation systems are 34.4 and 6.6%, respectively. The remaining 16.4% of farmers stock fish in reservoir ponds and use a monoculture system for shrimp. Among the farmers who adopt the simultaneous tilapia-shrimp polyculture system, 76.9% released tilapias directly into shrimp ponds, and 23.1% stocked tilapias in cages suspended in shrimp ponds. Tilapia-shrimp polyculture is practiced in a wide range of salinity levels from 0 to 30%. Tilapias used in the polyculture include red tilapia (Oreochromis spp.), Nile tilapia (O. niloticus), and Mozambique tilapia (O. mossambicus). The survey revealed that shrimp production and economic returns from the two simultaneous polyculture systems and in sequential polyculture systems were higher than those in their respective shrimp monoculture systems practiced before. Also shrimp production and economic returns from these polyculture systems were higher than those in the crop rotation polyculture system and in the currently practiced monoculture system. Many farmers responded that tilapia-shrimp polyculture could improve water quality in shrimp ponds, reduce diseases, and reduce the use of chemicals. In the direct style of tilapia-shrimp polyculture, about 40% farmers believed tilapias compete for feed with shrimp, while the remaining 60% were not aware of such feed competition. The major reasons given by Vietnamese shrimp farmers for not growing tilapia in shrimp ponds are that tilapia would compete for the costly shrimp feeds, water quality in shrimp ponds was good enough and there was no need to use tilapia to improve water quality due to low shrimp stocking density, and added tilapia might bring dissolved oxygen down thus adversely affecting shrimp growth. It can be concluded from the survey that polyculture of shrimp with tilapias may provide an alternative approach for shrimp farming, which could ultimately lead to a more sustainable shrimp industry. However, further research is needed on the merits for converting from shrimp monoculture to polyculture with tilapia.