Nile tilapia feeding in earthen ponds: evaluation of the nutritional value of some agro-industrial by-products and feeding practices

When rice bran and brewery draff were used as a single diet, the analysis of the body composition of tilapia showed significantly (P0.05) more moisture (76 to 81 percent, against 72 to 78 percent while using compound diets). The best diet in terms of growth and body composition of tilapia appeared to be one containing 30 percent rice bran, and brewery draff, cotton seed cake, soya oil meal and groundnut seed meal incorporated at 17 percent level each. For the practical distribution of the feeds in ponds, the results of another set of trials were the following: the validity of Marek's feeding table was confirmed for feeding of fish in the size range studied; i.e., from 5.3 percent of fish biomass per day for fish weighing 10-20 g, to 2.8 percent for those weighing 70-100 g. When the food was applied at six meals per day, weight gain was 1.4 times better than at three meals per day. The use of pellets rather than powdered feed reduced the feed conversion ratio from 3.0 to 1.8 and improved fish production (2.7 t/ha/yr, against 1.7) significantly (P0.05) and protein and energy retention efficiencies (36 and 19 percent, against 22.4 and 13.1 percent, respectively). Likewise, growth and retention efficiency of the supplemental feed (A) protein in tilapia was significantly improved (P0.05) by pond manuring with an equivalent of 180-kg dry matter of cow dung per day (F); the additivity effect of fertilization and supplemental feeding was observed for total fish production (i.e., 2.9 t/ha/yr. for A + F treatment approximately equal 2.2 t of treatment A + 0.8 t of treatment F). Two trials were conducted on predation by Hemichromis fasciatus of tilapia in ponds. All tilapia fry weighing less than 7 g were effectively eaten by adult (40 g) Hemichromis. The latter showed total abstention towards supplemental feed unlike their fry which grow well when fed with Tilapia feed. The overall analysis of the results for the site of the present research work (altitude 1,100 m, mean annual water temperature 24 deg C) showed that the best growth of tilapia daily growth coefficient of about 2.5 percent/day was registered from March to July