EFFECT OF DIETARY-PROTEIN LEVEL ON PUBERTY, OOCYTE GROWTH AND EGG CHEMICAL-COMPOSITION IN THE TILAPIA, OREOCHROMIS-NILOTICUS (L)

Oreochromis niloticus were maintained on 5 isocaloric diets of different dietary protein levels (10, 17, 25, 32 and 40%). In Expt. 1, O. niloticus (initial mean weight approximately 0.3 g) maintained on diets of 10 and 17% protein levels showed lower growth rates compared to those on the higher protein levels and none reached puberty. In Expt. 2 (initial mean weight approximately 3 g), only those receiving 10% dietary protein level gave similar results; fish fed 17% reached puberty. Fish fed higher protein levels (32 and 40%) reached puberty at an earlier age, with oocytes growing and maturing faster, than those fed lower levels (less than or equal to 25%). The former also showed higher growth rates, lower food conversion ratios and higher survival rates. When the onset of puberty and the rate of oocyte maturation were evaluated in relation to size (regardless of age), there were no significant differences among the treatments, suggesting that dietary protein may have influenced oocyte growth and puberty by its effect on growth. The chemical composition of post-vitellogenic oocytes, expressed as percent protein, lipid, moisture, and essential amino acids (mg in 100 mg protein), was not significantly different among the different dietary treatments.