EFFECTS OF DIETARY LIPID SOURCE
ON SPAWNING PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) BROODSTOCK
REARED AT DIFFERENT WATER SALINITIES
A.M. El-Sayed, C.R. Mansour, A.A.
Ezzat
The effect of dietary lipid
source and water salinity on spawning performance of Nile tilapia broodstock
and growth of their larvae was studied. Three isonitrogenous (35% cp),
isocaloric (400 kcal/100 g) diets containing three different oil
sources; soybean oil (SBO), fish oil (FO), and soybean
oil/ fish oil mixture (Oil mix) were prepared. The diets were fed to
duplicate groups of broodfish
(19.2 g) reared at three water salinities (0, 7 and 14 ppt), at a
females:male ratio of 3:1, to satiation, twice a day for 165 days. The size at first
maturation and was not significantly
affected by dietary oil source and water salinity. Spawning intervals of
broodfish reared at 0%o were not
significantly affected by dietary oil source. At 7 ppt and 14 ppt, fish fed FO
or Oil mix spawned at shorter intervals, and more frequently than those fed
SBO. The inclusion of FO in the diets increased the absolute fecundity and number
of eggs per spawn at each salinity.
The relationship of dietary oil source and water salinity on egg size was significant;
but showed irregular trends. The chemical composition of broodstock muscles,
eggs and fry were not significantly affected by dietary oil source and
water salinity. At 0 ppt, egg hatchability, days to hatch,
yolk sac absorption time and larval weight were not significantly
affected by dietary oil source. Eggs produced from broodstock fed SBO at 7
and 14
ppt needed more time for hatching and yolk-sac absorption and resulted in
poorer larval weight than those fed FO or Oil mix. This result revealed
that Nile tilapia broodfish reared in brackishwater (7 and 14 ppt
salinity)
require fish oil (a source of dietary n-3 HUFA) for optimum
spawning performance, while plant oil (SBO) may meet the requirements of broodfish
reared in freshwater (0 ppt).
(Oceanography Department,
Faculty of Science, University of Alexandria, Alexandria, Egypt, e-mail: a.elsayed@uaeu.ac.ae)