Evaluation of a man-made shelter's effects on survival and growth of Heterobranchus longifilis fry under cage culture

The effects of shelter made from inert synthetic shade materials on the survival and growth of Heterobranchus longifilis fingerlings were evaluated under cage (lm(3)) culture conditions in man-made Lake Ayame (Cote d'Ivoire) from September 2003 to March 2004 (180 days). In the first experiment, fishes (initial mean weight: 0.9 +/- 0.1 g; density: 100 fishes/m(3)) were reared during 90 days in either unsheltered or sheltered (white, blue or black synthetic shade material) cages. Survival and final mean weight were not affected by the colour of the shelter but were significantly higher (p<0.05) when shelter was provided (70.9-74.0\% and 16.2-17. 1g for sheltered cages vs 64.0\% and 11.8g for unsheltered). During the second experiment (90 days), H. longifilis (initial mean weight 0.9 +/- 0.1 g) were reared at four different stocking densities (100, 200, 500 and 1000 fishes/m3) in both sheltered and unsheltered cages. Survival and final mean weight noted were better in the sheltered cages. In both sheltered and unsheltered cages, these parameters were better for cages of 100 fishes/m3 and worst for cages of 1000 fishes/m3. In the third experiment (stocking density: 100 fishes/m(3)), H. longifilis of four different initial mean weight (13.2 +/- 1.3g, 25.2 +/- 2.5g, 40.3 +/- 4.0g and 60.3 +/- 6.0g) were reared during 60 days in either unsheltered or sheltered cages. Results showed two different effects of the shelter on survival and final mean weight of fishes: (1) positive effect for fishes weighting from 13.2 to 29.2g, and (2) negative effect for fishes weighting from 60.3 to 92.0g.