The effects of fertilization and water management on growth and productionof Nile tilapia in deep ponds during the dry season

Fertilization guidelines developed for shallow ponds (1 m) with controlled depths were tested in deeper (2.5 m) ponds to determine effectiveness of th ese guidelines for culture of Nile tilapia Oreochromis niloticus. Twelve po nds of 2.5-m depth were used in four treatments: (A) weekly fertilization w ith water addition; (B) weekly fertilization without water addition; (C) on e early fertilization without water addition; and (D) fertilization frequen cy dependent on nutrient concentrations, without water addition. Sex-revers ed Nile tilapia were stocked at 2 fish/m(2) with an initial weight of 15 g, and harvested after 234 d. Depth of water declined from 2.4 m to 1.6 m ove r the experiment in ponds without water addition. Fish growth rate was sign ificantly higher in treatments A and B (0.86 gld), than in other treatments , as was yield (3,830 kg/ha). Treatment C was lowest in growth (0.086 gld) and yield (168 kg/ha), with treatment D intermediate. Fish growth rates and yields were strongly correlated to manure input (R-2 = 0.89 and 0.94, resp ectively), and residuals were not correlated to any physical or chemical va riables. Growth and yield in these deep ponds were somewhat lower than thos e in previous experiments for shallow ponds with regular water inputs. Howe ver, stagnant ponds did not accumulate nutrients and metabolites at rates h igher than ponds with controlled water depths.