Livestock-Based Farming Systems, Renewable Resources and the Environment
An experiment was carried out in the research farm of An Giang University from January to April 2011.to compare integrated culture of Tilapia (Oreochomis niloticus) and Common carp (Ciprinus carpio) in an intensive indoor system with earthworms as feed, with an outdoor natural pond system, using biodigester effluent as fertilizer and duckweed as feed supplement. There were four treatments with three replicates in a completely randomized design with mixed stocking of Common carp and Tilapia (50: 50) at low and high densities (3 or 5 fish//m2 in the natural ponds and 60 or 100 fish/m3 in the intensive indoor system. In the outdoor system the fish were raised in natural ponds (4m2), seeded with duckweed and fertilized with biodigester effluent. In the indoor system, the fish were raised in PVC tanks (0.5m3) in an enclosed building and fed with earthworms.
Growth rates at the higher stocking rate were lower for the Common carp in the pond system and tended to be lower for the Tilapia as compared with the low stocking rate. In the indoor system where the fish were fed ad libitum, the growth rates were less affected by stocking density. In the outdoor pond system growth rates were much higher for the Tilapia than for the Çommon carp. In contrast, in the intensive indoor system, there were no differences between the two species. The Tilapia gained from 0.95 to 1.32 g/day at high and low densities in the natural pond system but only 0.26 and 0.33 g/day in the intensive system. In the natural pond system the net fish yields were equivalent to 9 and 10 tonnes/ha/year for the low and high densities, respectively. Environmental pollution, as measured by concentrations of total ammonia-N and nitrite in the water, was some 50% greater in the intensive system. An economic analysis, on the basis of gross returns from the fish less the variable costs (fingerlings and feed), showed positive margins for all species/density combinations in the natural pond system compared with the negative margins for the intensive indoor system.