Effect of selection for muscle lipid content on body shape, fat deposition and dressing yields in rainbow trout

A two-way selection for muscle lipid content was performed on pan-size fish using a non-destructive measure of muscle lipid content in live fish (Distell Fish Fatmeter®). The present study aimed at characterising direct and indirect responses after three generations of selection at the size where selection was applied as well as in larger individuals. Six experimental progeny were produced. Breeders of each selected line (lean, L and fat, F) were mated according to a factorial design to produce 4 diploid groups: lean (LL2), fat (FF2) and two reciprocal hybrids (LF2 and FL2). Triploids (LL3 and FF3) were also produced to obtain large sterile fish. Each group was reared in 3 replicated tanks, examined at 12 months (pan-size; all groups) and 19 months old (2 kg, triploids only). Main results demonstrated that there was no indirect effect of selection on growth performance, irrespective of the age. Body shape however was modified, FF fish being more rotund with a smaller relative head length. Muscle lipid content varied in a wide range according to the line, hybrids exhibiting intermediate values (LLb(FL=LF)bFF). There was no effect of triploidy on this trait. Increase in muscle lipid content was associated with an increase of subcutaneous fat deposition but a decrease in visceral fat content. Values of the majority of traits were intermediate in hybrids. In large fish, carcass and fillet yields were better in FF fish. Effects of muscle lipid content on flesh quality traits are presented in a separate abstract (Lefevre et al.).