CULTURE OF NILE TILAPIA IN CIRCULARS AND SQUARES NET CAGES IN TWO STOCKING DENSITIES

The present experiment evaluated the effect of stocking density on the zootechnical performance of Nile tilapia (Oreochromis niloticus) cultured in 3.14 m(3) round net cages and 3.00 m(3) square net cages. Stocking densities of 100 and 150 fish m(-3) (f. m(-3)) and both types of net cages were used as different treatments each one with five repetitions, with initial fish weights and lengths average of 80.00 +/- 2.56 g and 15.25 +/- 0.18 cm, respectively. During the experiment (112 days), fish were fed six days a week and four times a day with a commercial balanced floating 32% crude protein ration by a 5.5% biomass feed rate until individuals main weight reach 300 g, and gradually reduced and administered two times a day from this moment until a biomass feed rate of 2.0% at the end of the experiment. An economic analysis of each treatment cultures also was done using fish, ration and hand-men work costs. Fish final mean weight analyses showed an improvement in 100 f. m(-3) circular net cages. The fish average daily gain, food efficiency and apparent food conversion were significantly better in 100 f. m(-3) circular net cages. With this work, it was demonstrated a better development of Nile tilapia in a low stocking density in round net cages. In addition, net income per kilogram of produced fish also was the highest in circulars low density net cages.