Effects of dietary fish oil replaced with rapeseed oil on the growth,fatty acid composition and skin color of large yellow croaker(Larimichthys crocea)

An 8-week feeding trial was conducted to investigate the effects of dietary fish oil replaced with rapeseed oil on growth,muscle fatty acid compositions and skin color of large yellow croaker(initial weight 13.56±0.05 g).Five isoproteic and isolipidic experimental diets were formulated with 0%,25%,50%,75% and 100% replacement of fish oil by rapeseed oil.Results showed that these replacements did not significantly influence the survival rate(SR)and specific growth rate(SGR)(P0.05).However,the feed conversion ratio(FCR)was increased with the increasing of replacement levels.Furthermore,FCR in the group of 100% rapeseed oil was significantly higher than that of 100% dietary fish oil(P0.05).No significant difference was observed in the whole body compositions(P0.05).The concentrations of C18∶ 0,C18∶ 1,C18∶ 2n-6,C18∶ 3n-3 and the saturated fatty acid(SFA),except C20∶ 4n-6 and C22∶ 5n-3 in muscle,were elevated with the increasing of dietary rapeseed oil levels.There were no significant differences in yellowness(b*)of dorsal and ventral skin among the five treatments(P0.05).Lightness(L*)of the dorsal skin in the treatment with 100% dietary rapeseed oil was significantly higher than that with 100% dietary fish oil(P0.05).However,L* of the ventral skin was not significantly different among the all treatments(P0.05).Higher redness(a*)of ventral skin and lower a* of dorsal skin were found in fish fed with 0% rapeseed oil.This study suggested that there were no significant effects of replacement of dietary fish oil by rapeseed oil on growth and body composition.However,the fatty acid composition of muscle and the skin color were significantly influenced.