Growth response and survival of Heterobranchus longifilis cultured at different water levels in outdoor concrete tanks

Thirteen-day-old hatchery-raised fry obtained from hormonally-induced spawns of mature African catfish H. longifilis broodstock were introduced to three different water levels (0.35, 0.50 and 0.65 m) in four replicates in 12 units of 2x2x1m3 outdoor concrete tanks. The fry were similarly stocked initially at 50 fry m-2 and later thinned down to 5 fish m-2 and cultured for 6 months. Fish were fed twice daily with commercial pellet feeds (Coppens™) while adjusting the feeding rate from 10 to 4% body weight and pellet size from 0.2 to 4.5 mm. The effects of pond water levels were evaluated in growth responses and survival. Water quality variables were similar (p > 0.05) in all compartments. Temperature, dissolved oxygen and pH were at the optimum level for fish. The results reveal significant (P < 0.05) treatment effects on growth performances. Fish kept at the highest pond water depth (0.65m) were heavier (P < 0.05) and had a higher specific growth rate (P < 0.001) than the others. Food conversion ratio and survival rate were unaffected by the experimental treatments. ANOVA revealed significant differences (P