Effects of dietary protein
level on spawning performance of Nile tilapia (Oreochromis niloticus)
broodstock reared at different water salinities
A.-F.M. El-Sayed, C.R. Mansour, A.A. Ezzat-2003
Aquaculture, 220(1-4): 619-632
Abstract:
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 (0 ppt, 7 ppt and 14
ppt) 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 0 ppt
reached their sexual maturity at bigger sizes than those reared at 7 ppt and
14 ppt. At 0 ppt, spawning intervals were not significantly affected by
dietary protein levels. At 7 ppt and 14 ppt, 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 7 ppt
and 14 ppt 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 7 ppt and 14 ppt 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 0 ppt, 7 ppt and
14 ppt salinity. It also indicated that spawning performance and larval
growth were better in freshwater than at 7 ppt and 14 ppt.