Long term partial replacement of dietary fish oil with rapeseed oil; effects on egg quality of Atlantic salmon Salmo salar

The use of vegetable oil in broodstock diets and its effect on gamete quality was investigated. During September 2002, 315 Atlantic salmon (2nd sea winter) were individually tagged and divided amongst three sea cages. The fish were fed a broodstock diet with 100% South American fish oil (at a dietary lipid level of 27.6%) in one treatment group and with 50% (the rest replaced with rapeseed oil) in the others. The fish were weighed and measured in November 2002, May 2003, and July 2003. Maturing fish were transferred to fresh water in October 2003 and individual fecundity and mean egg weights were measured. Dietary treatment did not affect egg number or egg weight. The eggs from a sub-set of females from each treatment were fertilised using a pool of milt from three males of the same treatment. Samples of the pre-fertilised eggs underwent fatty acid, astaxanthin and proximate analysis. The fatty acid profiles of the eggs and fry differed between dietary treatment, the rapeseed oil treatment producing lower levels of DHA (22:6n-3) and EPA (20:5n-3) and higher levels of 18:1n-9, 18:2n-6 and 18:3n-3, but rates of fertilisation, eyeing, hatching, survival to first feeding and the fry weight at first feeding did not. These results suggest that it is possible to replace a portion of the fish oil (South American) with rapeseed oil in a broodstock diet without compromising the early survival and initial growth of offspring, although there could be implications for some developmental processes not tested for in this study.