Effects of dietary protein level on spawning performance of Nile tilapia (Oreochromis niloticus) broodstock reared at different water salinities

摘要

Effects of dietary protein level and water salinity on spawning performance of Nile tilapia broodstock and growth of their larvae were studied. Four isocaloric (400 kcal/100 g) diets containing 25%, 30%, 35% and 40% crude protein were prepared. The diets were fed to broodfish (25.7 g) reared at three water salinities (0parts per thousand, 7parts per thousand and 14parts per thousand) at a female/male ratio of 3:1, to satiation twice a day for 195 days. The size at first maturation increased with increasing dietary protein at all salinities. At 25% and 30% protein levels, broodstock reared at 0parts per thousand reached their sexual maturity at bigger sizes than those reared at 7parts per thousand and 14parts per thousand. At 0parts per thousand, spawning intervals were not significantly affected by dietary protein levels. At 7parts per thousand and 14parts per thousand, spawning intervals significantly decreased with increasing dietary protein level. Spawning frequency and number of eggs per spawn were increased with increasing dietary protein level. The total number of spawnings per female and absolute fecundity were better in fish fed 40% protein in freshwater than at 7parts per thousand and 14parts per thousand salinity. The relationship of dietary protein and water salinity on egg size was significant, but showed irregular patterns. The chemical composition of broodstock muscles, eggs and fry were not significantly affected by dietary protein and water salinity, except for body water and crude protein of broodstock which were significantly affected; but showed irregular trends. At each water salinity, egg hatchability was linearly increased with increasing dietary protein level. Eggs produced from broodstock fed 25% protein at 7parts per thousand and 14parts per thousand needed more time for hatching and yolk-sac absorption and resulted in poorer larval weight than those reared in freshwater. Fry growth was improved with increasing protein level at all salinities. This result revealed that 40% dietary protein is required for optimum spawning performance of Nile tilapia reared at 0parts per thousand, 7parts per thousand and 14parts per thousand salinity. It also indicated that spawning performance and larval growth were better in freshwater than at 7parts per thousand and 14parts per thousand.