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Abstract
Two techniques for producing Nile tilapia. Oreochromis niloticus, fry suitable for sex-reversal were evaluated: (1) broodstock placed in 8-m2 fine-mesh (1.6 mm) suspended net enclosures apas from which fry could not escape, and (2) broodstock placed in 8-m2 large mesh (6.4 mm) hapas from which fry could escape into a 0.67-mm deep 20-m2 concrete tank. There was no significant difference (P > 0.05) in the number of fry less than 14 mm produced in the large- or fine-mesh hapas with an average of 286 fry/m2. However, fry produced in large-mesh hapas were significantly larger (10.9 mm; P < 0.05) than fish produced in fine-mesh hapas (9.4 mm) since they were free to forage over a greater area. There was a significant difference (P < 0.05) in the time required to harvest the fine-mesh (11.0 minutes) and the large-mesh (18.7 minutes) hapas since tanks with large-mesh hapas had to be drained for fry collection There was no difference (P > 0.05) in fry mortality during harvest averaging 1.3%. The large-mesh hapas produced the same number of fry as the fine-mesh hapas except the fry were larger. Consequently, the fry production period could be shortened which would enable a farmer to increase the number of production periods per year.