Effect of dietary protein level on spawning performance and amino acid composition of eggs of Nile tilapia, Oreochromis niloticus

Oreochromis niloticus were maintained on three purified, isocalorific diets of different dietary protein levels (10, 20 and 35%), with casein and gelatin as protein sources, The dietary protein influence on spawning interval, fecundity, relative fecundity (number of eggs per unit weight) and egg size at four successive spawnings was investigated. The protein, moisture, free and bound amino acid composition of the spawned eggs were determined. O. niloticus females fed 20 and 35% protein levels maintained their spawning cycle, whereas at 10% spawning intervals were prolonged after about 4 months of feeding. Females fed 20 and 35% protein diets produced a higher number of eggs per spawn than those fed 10%, especially at later spawnings, But relative fecundity and egg size did not differ significantly between the treatments. The amount of protein in eggs of females maintained on 35% protein diet was significantly higher than in others, However, the moisture content of the eggs did not vary among the diets. Of the free amino acids, methionine, valine, tyrosine, serine, glycine and proline were influenced by the dietary regime. The total (free + protein bound) individual amino acids in the eggs were not affected by dietary protein level. However, the total overall amino acid pool of eggs in the 35% protein level was higher than in the others.