INFLUENCE OF PROTEIN-CONTENT OF BROODSTOCK DIETS ON LARVAL QUALITY AND PERFORMANCE IN NILE TILAPIA, OREOCHROMIS-NILOTICUS (L)

Performance of mature Nile tilapia females reared on three isocaloric, purified, diets of 10, 20 and 35% crude protein (CP), for a minimum p eriod of 4 months, in relation to fertilizability, hatchability and la rval quality was investigated. Care was taken to minimize the influenc e of males on egg and larval quality, and to ensure that the results r eflect the nutritional history of the brooding females. The eggs of fe males reared on the 10% CP diet were not fertilized. The means of the number of eggs per spawn, egg diameter and percent fertilizability wer e 359 +/- 31 and 398 +/- 39, 2.29 +/- 0.05 and 2.31 +/- 0.05 mm, and 7 9.8 +/- 4.2 and 83.8 +/- 3.9 for females fed on 20 and 35% CP diets, r espectively. The differences between the diets for the above parameter s were not significant. However, the percent hatchability (20% CP 41.7 +/- 5.1; 35% CP 68.7 +/- 3.6) of the eggs and the percentage of norma l larvae (20% CP 41.8 +/- 4.4; 35% CP 59.8 +/- 2.8) from the females o n 35% CP diet were higher (P < 0.05). No significant differences were observed in mean total length, head width, rate of yolk utilization an d in the response to a cold stress test of larvae from the two dietary levels. Significant differences were, however, observed in the free a mino acid content of larvae from the two groups of females, but not in other chemical traits such as total protein or moisture content. A re lationship was evident between fertilizability and hatchability of egg s to their free amino acid content.