EFFECT OF DIETARY FISH OIL REPLACEMENT WITH PLANT OILS ON GROWTH PERFORMANCE AND GENE EXPRESSION IN JUVENILE RAINBOW TROUT (ONCORHYNCHUS MYKISS)

An eight-week feeding trial was conducted to evaluate the effects of total (100%) replacement of dietary fish oil with alternative lipid sources in juvenile rainbow trout. Six iso-nitrogenous and iso-lipidic experimental diets were formulated: CO (14%) -cod liver oil; SSO (14%) -safflower seed oil; SBO (14%) -soybean oil; LO (14%) -linseed oil; SBO (7%) + LO (7%) -a blend of soybean oil and linseed oil; and SSO (7%) + LO (7%) -a blend of safflower seed oil and linseed oil. Growth performance [specific growth rate (SGR), weight gain (WG), food conversion ratio (FCR) and survival rate (SR)], growth hormones [growth hormone (GH-I), insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II)], immune transforming growth factor-beta (TGF-beta) and antioxidant [superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT) and glutathione S-transferase (GST)] response, and heat shock protein 70 (HSP70) mRNA levels were determined in muscle and liver. Our data indicated that final weight, weight gain, FCR and SGR showed significant difference among the six dietary treatments (P<0.05) while there were no significant differences in survival rate between the rainbow trout from supplement fed groups and control group. HSP70 mRNA level expression in muscle was higher in fish fed SSO (P<0.05) while highest level in liver was obtained from fish fed SBO compared to the other treatments (P<0.05). There were no significant differences among treatments for TGF-beta mRNA expression level in muscle and liver. In conclusion, growth performance and expression levels of growth hormones, antioxidants, HSP70, except TGF-beta were affected by five separate lipid sources. In addition, LO positively increased growth performance of juvenile rainbow trout by means of preventing oxidative stress and HSP70 and, enhanced expression of growth hormone related gene.