الفهرس 
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Abstract
This experiment was carried out indoor installations of the fish research
laboratory, Faculty of Agriculture, Minufiya University, Egypt; it’s started on June
20th, 2010 until October 10th, 2010 in order to investigate the effect of replacing fish
meal protein in Nile tilapia, Oreochromis niloticus (L.) diets and utilizing of
Cottonseed meal in grow-out phase.
The main objectives of this study was to determine the effect of
replacement of fish meal by Cottonseed meal in practical diets of Nile tilapia
fingerlings on growth performance, feed utilization, body composition and some
biological and hematological measurements of Nile tilapia. Fish of an average
initial weight of 7.7 g and initial length of 7.5 cm were stocked in 15 glass aquaria
(200 l each) at a rate of 20 fish per aquarium.
Fish meal (46.68 % 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 5 %,
and then gradually reduced to 2 % of the total fish biomass daily, for a period of 16
weeks.
The results of this study revealed that, the fish fed diet B had significantly (P
0.01) the best average body weight, gain in weight (g/fish), gain in weight %,
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specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio
(PER) and feed consumed (g/fish) from those of fish fed control diet A and all other
diets. The same parameters of fish fed diet C were not significantly different (P
0.05) from those of fish fed the control diet A. Condition factor (K), hepatosomatic
index (HSI), Gonadosomatic index of female (GSI) and survival rate % of the fish
fed experimental diets B and C were not significantly different (P 0.05) from
those of fish fed the control diet A.
Incorporation of cottonseed meal in the diets did not affected the
gonadosomatic index of male Nile tilapia. The best values of hematocrit % and
hemoglobin % were recorded with groups of fish fed diet A (control) and diet B (25
% cottonseed meal) and then decreased significantly (P 0.01) with increasing
cottonseed meal level in diets C, D, and E. Chemical composition of fish flesh
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 the control diet A.
from the above results and the economic evaluation of the study it can be
concluded that, up to 50 % of fish meal protein can be replaced by Cottonseed meal
protein in fingerlings Nile tilapia diets without decreasing the growth performance
and feed utilization parameters and seems to be the lowest cost to maximize the net
profit without depressing the growth.