Researching Alternatives to Fish Oils in Aquaculture
RAFOA has established that, with judicious care, much if not all of the fish oil currently used in the production of salmon, rainbow trout, sea bream and sea bass can be replaced with a blend of vegetable oils without comprising the growth performance of any of the species. The substantial changes in the fatty acid compositions of the fillets resulting from the VO blend can be readily and largely reversed in all species with a "finishing diet" of fish oil.
Thus, much of the FO used in current aquaculture is wasted in the sense that it can easily be replaced with more readily available and sustainable VO. This, as evidenced by the RAFOA findings, is logical since most of the oil used in fish diets is catabolised by the fish to provide growth for energy. A suitably blended VO diet can be catabolised and provide as much energy for growth as a fish oil diet, provided the EFA requirements of the fish are met.
In the case of RAFOA the EFA requirements were provided by the lipid (oil) in the fish meal component of the diet. Thus, replacing both fish meal and fish oil simultaneously in fish feeds may be more challenging and difficult to achieve, though findings in RAFOA offer promising approaches to achieving this. Irrespective, there is no reason to continue the current excessive and wasteful use of increasingly limited and possibly non-sustainable FO in fish feeds.
Blends from sustainable VO are perfectly acceptable Alternatives for most but not necessarily all of the FO currently used in aquafeeds. Moreover, an important by-product of substantially replacing fish oil in aquafeeds with VO blends is that levels of persistent organic pollutants, including PCBs and dioxins emanating from FO are markedly reduced in the fish (as evidenced by related research carried out by RAFOA participants from resources outwith RAFOA).
We are pleased to note that substantial replacement of FO with VO blends in aquafeeds is already being implemented by the feed industry and trust that RAFOA has played a significant part in achieving this desirable development. A caveat to this general conclusion is that RAFOA has shown that substituting FO with VO in salmon feeds increases the incidence of eye cataracts in salmon, but in none of the other species. In addition, some blood parameters suggest that fish grown on VO diets may be under somewhat increased stress.
Therefore, in future studies with fish grown on diets with FO replaced with VO, particular care should be given to monitoring the health and welfare of the fish.