Influence of dietary protein level on ovarian recrudescence in Nile tilapia, Oreochromis niloticus (L.)

Abstract

Ovarian recrudescence was investigated in Nile tilapia, reared on isocaloric, semi-purified diets of 10, 20 and 35% protein content, for 2 and 4 month periods. Females immediately after spawning were used with a view to ensuring that all individuals investigated would have ova in a regressed state initially, so that subsequent changes could be correlated to dietary protein affects. In females reared for 2 months, the dietary effects on ovarian recrudescence became most evident only by Day 14, when a significantly higher percentage of Stage 4 oocytes (diameter > 2.4 mm, pear-shaped, bright yellow, post vitellogenic oocytes) were present in the 35% protein fed females as compared to those fed the 10% protein diet. In females reared on the diets for 4 months, comparable differences were evident on Day 7 after spawning. Here ovarian recrudescence of 10% protein fed females was slower than in females maintained on 20 and 35% dietary protein levels. In females reared for 2 and 4 months on the experimental diets. GSI, however, did not vary significantly amongst fish fed 10, 20 and 35% diets, in the regressed and recrudescing ovaries at Day 7 and Day 14. There was evidence to indicate that even when the females are reared on a sub-optimal diet (e.g. 10% protein) they make an attempt to go through the recrudescence process, perhaps by utilizing existing body reserves.