Effects of stocking density and water exchange rates on growth performances, production traits, feed utilization and body composition of mono-sex male Nile tilapia, Oreochromis niloticus (L.) cultured in concrete tanks

A 44-week randomized factorial design 2 x 3 x 2 ( two water exchange rates, three stocking density and two replicates) rearing trial was conducted in concrete tanks with average initial weight and length of 7.5 ± 1.2 g/fish and of 8.9 ± 0.5 cm/fish of mono-sex male Nile tilapia, Oreochromis niloticus , to examine the effects of two water exchange rates and three stocking density on growth performances, production traits, feed utilization and body composition. Twelve concrete tanks 4 m 3 each were stocked with either 200, 300 and 400 fish for each tank to give a stocking rate of 50, 75 and 100 fish /m 3 , respectively and mentioned at 8L/min. or 12 L/min. water exchange rates. The results revealed that, growth performance and feed utilization parameters were significantly (P £ 0.01) the best at the lowest stocking density. No significant differences (P > 0.05) were found between water exchange rates in terms of growth performance, feed utilization and all production traits. The lowest stocking density (50fish/m 3 ) had significantly the best feed utilization parameters. There were no significant differences between it and the stocking density of 75fish/m 3 . Whole fish body composition % of protein, fat and ash contents were significantly (P £ 0.05) influenced by stocking density but did not influenced by water exchange rates. From the above results it can be concluded that, stocking density of 75 fish /m 3 of mono-sex male Nile tilapia reared at either 8L/min or 12L/min. water exchange rates exhibited the highest net profit and would seem to be the most desirable density under this system conditions.