The main objective of this study was to determine the effect of partial and total replacement of fish meal by cottonseed meal in practical diets of Nile tilapia fingerlings on growth performance, feed utilization, body composition and some biological measurements of Nile tilapia, Oreochromis niloticus (B). Fish of an average weight 18.1 ±0.2 g were
stocked in 15 glass aquariums (80 L each) at a rate of 15 fish per aquarium. Fish meal (40 % of the diet) was used as the sole source of animal protein in the control diet. Percent replacement of fish meal by cottonseed meal on the
basis of crude protein were as follows: 0 % (control diet A), 25 % (diet B),50 % (diet C), 75 % (diet D) and 100 % (diet E). Diets were fed to fish at a rate of 4 %, then gradually reduced to 3 % of the total fish biomass daily,
for a period of 14 weeks. The results of this study revealed that, the fish fed on diet B had significantly (P ≤ 0.01) best average body weight, average body lengrh, specific growth rate (SGR), weight gain %, feed conversion
ratio (FCR), and protein efficiency ratio (PBR) from those of fish fed on control diet A and all other diets. The same parameters of fish fed on diet C were not significantly different (P > 0.05) from those of fish fed on the control diet A. Condition factor (K), hepatosomatic index (HSI) and survival rate % of the fish fed experimental diets B and C were not
significantly different (P >0.05) from those of fish fed on the control diet A.The best values of hematocrit % and hemoglobin % were recorded with groups of fish fed on diet A (control) and diet B (25 % cotton seed meal)
and then decreased significantly (P ≤ 0.01) with increasing cotton seed meal level in diets C, D, and E. Body composition of crude protein and crude fat (wet and dry basis %) and apparent digestibility coefficient of crude protein and crude fat of the fish fed experimental diets B and C did not differ significantly (P> 0.05) from those of fish fed on the control diet A.
Therefore these findings suggest that up to 50 % of fish meal protein can be replaced by cotton seed meal protein in fingerlings Nile tilapia diets.