Research Shows Salmon Can Get Too Fat

The salmon store body fat in the wrong places, says NIFES research scientist Bente E. Torstensen.

NIFES has led the first feeding trials in which farmed salmon were fed an almost exclusively vegetarian diet. The results, which have just been published in the British Journal of Nutrition, suggest that such a diet seem to be lacking essential nutrients for large growing salmon.

Plant food for fish

Farmed salmon are traditionally fed a marine-based diet in the form of fish-oil and fish-meal. In place of this, NIFES scientists formulated a diet in which 70 per cent of the fish-oil was replaced by vegetable oil and 80 per cent of the fish-meal with plant protein, and fed it to Atlantic salmon for 12 months.

The feeding trial showed that salmon do not do well as vegetarians.

The salmon stored more fat in their blood, liver and around internal organs. It is normal for salmon to have a lot of fat in their bodies, but not just there. Salmon basically have lean livers, says Mr Torstensen.

So salmon, which are naturally fatty fish, seem to be capable of developing obesity.

We have seen the same phenomenon as we find in humans who are in the process of developing metabolic syndrome. The salmon become fat in the wrong places, and this can cause metabolic imbalance and have negative health effects.

Metabolic syndrome is a collective term for various conditions that can lead to type two diabetes and cardiovascular disease, among other ailments.

In other words, one could imagine that Atlantic salmon could develop heart disease if they have too much raw material derived from plants in their diet without re-evaluating their essential nutrient requirement levels.

Finding the limit

The trials form part of the European Unions AquaMax project, in which NIFES and 32 other institutions in 14 countries have been studying fish meal and fish oil replacement for farmed fish, and their effects on the health of both the fish and consumers.

The rapid growth of the fish-farming industry means that in the future, feeding salmon a marine-based diet will not be a sustainable strategy. In 2030, about half of the worlds production of seafood will come from aquaculture.

With these results, we can conclude that too much vegetable food can have negative effects for the salmon, but just where the limits lie is something we still need to find out, says Mr Torstensen.

Nor do the scientists know at present whether bigger stores of fat around internal organs will have the same negative effects on health in salmon as in human beings.

That is something that we hope to find out in our next experiments, says Mr Torstensen.