In an experiment carried out in the fish wet lab of the Faculty of Agriculture,
Ain Shams University. 360 fish fingerlings (Oreochromis aureus) with an average
initial weight of 3g! fish were used. The fish were randomly distributed in 18 twenty
liter fiberglass tanks (20 fish each). The tanks were a part of closed system provided
with biological and mechanical filters to keep constant water quality in all tanks.
Water temperature was kept constant at 27" C throughout the experimental period (8
weeks) by an electrical thermo regulated heaters (4kW). Six experimental diets were
formulated to contain 31% crude protein and 4150 cal gross energy! kg, where diet 1
(control) contains fish meal and soy bean meal as a main sources of protein in the
diet. In the second diet, soybean meal protein was replaced by sweet lupin protein to
test the effect of replacing soybean meal by sweet lupin. and diets 3. 4. 5 and 6 were
designed to include only plant protein sources (soybean meal and sweet lupin)
supplemented with 0, 0.3, 0.6 or 0.9 % DL-methionine, respectively. Each diet was
fed daily to 3 tanks at a rate of 7% of fish body weight daily. During the experimental
period. fish were weighed every 7 days to. adjust feed amount. A sample of fish
fingerlings at the beginning of the experiment and the all fish at the end were
chemically analyzed to determine the differences in body composition. The results showed that fish groups fed diets containing both animal and
plant proteins (diet 1 and 2) had the highest significant weight gain (P<0.05). When
animal protein was replaced by plant protein without methionine supplementation
(group 3) fish final weight decreased to less than 50% of the control group. With
adding DL-methionine the growth performance parameter values (weight gain, SGR.
feedl gain. PER, PPV and the energy utilization) started to increase. Final body
protein was not significantly (P>0.05) affected by the type of protein used in diets.
Body fat content was decreased when sweet lupin was incorporated in diets. Ash did
not indicate any changes when protein source in the diets was changed. It seems that
soybean meal can be replaced by sweet lupin without adverse effects on fish
productive performance and supplementation of sweet lupin with DL methionine
improved growth rate and feed utilization of blue tilapia fingerlings (Oreochromis
aureus).