Abstract:
A 12-week feeding trial was conducted using Nile tilapia, Oreochromis niloticus (L.)
to evaluate the interactive effects of fishmeal replacement and salinity on growth,
feed utilization efficiencies and relative expression of growth related genes. Two
iso-nitrogenous and iso-energetic diets were prepared (32% protein). The control
diet included 15% fishmeal (FM diet) and fishmeal component in non-fishmeal diet
(NFM) was eliminated by a mixture of poultry by-product meal, high protein distillers
dried grains and distillers dried grains with soluble. The NFM diet was supplemented
with DL-methionine and L-lysine. Duplicated group of fish with initial mean
weight of 6 g, reared in four salinity levels (0, 4, 8 and 12 g/L) were fed one of the
two diets twice a day to near satiety. At the end of the experiment, growth, feed
utilization efficiency and expression of growth related genes were compared. The
specific growth rate (SGR), mean feed intake (MFI) and feed conversion ratio (FCR)
were not affected by the diets while salinity effects were significant. The fish in the
4 g/L salinity showed the highest SGR and MFI while fish in the 0 g/L treatment
showed the lowest FCR. Relative expression of hepatic IGF-I and IGF-II was regulated
by salinity but not by the diet. Expression of growth hormone receptor gene
was not affected by either diet or salinity. The present findings provide evidence
for the possibility of total fishmeal replacement in saline waters (0–12 g/L) without
compromising growth, feed utilization and body composition of Nile tilapia.
