Vegetable-fed salmon still yield healthful fat

AquaMax, a large international project with strong Norwegian participation, has studied the effects on the nutritional benefits of fish raised on a diet that substitutes vegetable feed ingredients for some of the marine ingredients. The project has generated new, important knowledge about the nutritional requirements of production species and what makes these fish safe and healthy for human consumption.

The project, a collaboration between 33 partners from 14 countries, was headed by the National Institute of Nutrition and Seafood Research (NIFES) in Norway. The objective was to develop fish feeds using maximum proportions of vegetable-based ingredients -- while still safeguarding fish welfare and ensuring that the fish products remain safe and healthful for consumers.

AquaMax has been a prime example of successful Norwegian participation in EU-funded research. Its results are now benefitting the Norwegian aquaculture.

Good source of healthful fats

The AquaMax researchers conclude that fully 70 per cent of the fish oil and 80 per cent of the marine proteins in conventional feed can be replaced with vegetable ingredients without any adverse effect on fish health.

Even with such a radically altered diet, salmon appear to retain their value as a good source of fatty acids that are healthy for humans.

Dietary dilemma

"Exchanging vegetable ingredients for fishmeal and fish oil involves taking a great many feed components into account," explains Project Coordinator Øyvind Lie, Director of NIFES.

Eating seafood can be seen as something of a trade-off. "We know we risk losing some of the beneficial marine omega-3 fatty acids in fish fat by altering the feed composition. Compared to vegetable sources, however, those same marine ingredients may contain more pollutants such as dioxins, PCBs and brominated flame retardants. We have observed substantially lowered amounts of dioxins in fish that are fed vegetable ingredients."

The AquaMax project examined whether production salmon can still be considered healthful food when raised on roughly 50 per cent vegetable feed.

"The risk of ingesting contaminants must be weighed against the health benefits of eating seafood rich in the marine omega-3 fatty acids EPA and DHA," points out Dr Lie. "This is a dilemma for pregnant women in particular."

Pregnant and vulnerable

The AquaMax researchers chose to focus on precisely that group: expectant mothers.

"Pregnant women and the children they are carrying are most vulnerable to pollutants such as dioxins -- yet they also have the greatest requirement for the nutrients in fish," explains Dr Lie. "Marine omega-3 fatty acids are especially important for both mother and baby."

In designing a diet for pregnant subjects, the researchers raised salmon on a customised feed in which large proportions of marine ingredients were replaced with vegetable meal. The salmon feed still contained some marine ingredients. The fish fillets were consumed by 62 pregnant women twice a week, from Week 21 of their pregnancy until giving birth. The babies were also followed up for their first six months.

The control group of 62 women, also pregnant, consumed the same amount of fish as they normally would have. "Where these women resided (in Southampton, UK), fish comprises a very small part of the overall diet," notes Dr Lie.

"The results were very encouraging. In the group that ate the test salmon fillets, omega-3 levels were elevated in both the mothers and their babies. Even though these test salmon had received less omega-3 through a feed based mainly on vegetable ingredients, the salmon meat still provided an excellent source of the healthful fatty acids."

Dietary advice depends on research

"This means we can raise salmon on feed with high proportions of vegetable ingredients. This in turn reduces our need for marine resources while at the same time maintaining a sufficiently healthy level of fatty acids and lowering the risk of pollutants. Knowledge like this is vital for the authorities who provide nutritional guidelines concerning public consumption of seafood."

Vegetable ingredients used in fish feed do contain pollutants, but the AquaMax project's preliminary results indicate that not much of these are carried over into the actual fish fillets. Comparatively more pollutants are transmitted from fish ingredients.

What do consumers think?

Part of the AquaMax project was to study consumer reactions to production fish eating feeds with different ingredients. Researchers examined media coverage of the issue and interviewed focus groups to get an idea of public opinion and understanding.

"Public opinion is highly relevant to the issue; unfortunately, the negative perceptions outnumber the positive," reports Dr Lie. But consumer thinking differed from country to country. The findings from this study provide the industry with insight into how it can better communicate with consumers.