Interactive effects of salinity and complete fishmeal replacement on growth, food consumption, and gene expression of hepatic IGF-I, IGF-II and growth hormone receptors in Nile tilapia,Oreochromis niloticus(L.)

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.