Tambaqui growth in response to stocking density in cages

The tambaqui Colossoma macropomum is rearing on different systems and environments and has shown good production in cages. The aim of this study was to evaluate the growth of tambaqui at different stocking densities in a lake supplied by rainwater and its effects on environmental quality. The experiment was conducted in consecutive phases: nursery at densities of 50, 100, 200 and 300 fingerlings m(-3) and growth at densities of 20, 40 and 60 juveniles m(-3). Water temperature, dissolved oxygen, pH and conductivity were monitored daily. Sediment and water samples were collected for analyses of nitrogen and phosphorus monthly. In the nursery, yield of 14,03 kg m(-3) was significantly higher for fish at 300 fingerlings m(-3). The highest weight gain was obtained at 50 fingerlings m(-3). Survival over 97% was observed in the nursery. In the growth phase, weight gain and specific growth were inversely proportional to densities. Feed conversion and condition factor were not influenced by the evaluated densities. The density of 20 juveniles m(-3) is more adequate to grow tambaqui in cages. Tambaqui cage culture did not alter the levels of nitrogen and phosphorus nutrients of lake water. Increased levels of organic matter, nitrogen and phosphorus in the sediment below the cages were verified without creating events of eutrophication. The results show that the tambaqui cage culture is viable in lakes provided with rainwater and can be integrated with multiple-use water services.