Effects of partial substitution of fishmeal by soybean meal in Nile tilapia (Oreochromis Niloticus) diet

The experimental trial was conducted in saline water to determine the replacement level of fish meal with locally available plant protein source, the soybean meal on growth performance, survival and body composition of Nile Tilapia (Oreochromis niloticus) juveniles reared in floating net cages. Four types of diet (35% crude protein) were formulated where fishmeal was replaced by soybean meal, partially up to 0%, 25%, 50% and 75% designated as treatment T1, T2, T3 and T4 respectively. The diet T1 was the control diet where a fish meal was the main ingredient and sole source of protein. A triplicate group of thirty healthy fish, juveniles (15.58g average initial weight) were stocked in each floating net cage (1.2 x 1.2 x 1.2m). Feeding was done at the rate of apparent visual satiation twice daily for a period of six weeks. At the end of the trial results indicates that there were no significant differences (P>0.05) in percent weight gain (%), specific growth rate (SGR %), average daily weight gain (g/ind/day), and feed conversion ratio (FCR) up to 50% fishmeal replacement by comparing with the control diet without soybean meal. However, deterioration in growth performance was noted in fish receiving more than 50% dietary soybean meal. Feed conversion ratio was poorer by increasing the soybean meal over 50%, T4 (2.81±0.74) and T3, (2.55±0.36), which is significantly different from T1 (2.21±0.12) and T2 (2.34±0.34). Survival was 94.99% in all the treatment groups. No significant differences (P>0.05) were found in fish final body carcass composition of protein, ash and moisture contents, but, the lipid level of the fish's body increased (P<0.05) significantly with an increasing fish oil and soybean meal in the diets. As a result, 50% soybean meal in the diet can substitute fishmeal without jeopardizing the growth and health condition of Nile tilapia