As the global population and its demand for seafood increases, more of our fish will come from aquaculture. Farmed Atlantic salmon are a global commodity and, as an oily fish, contain a rich source of the health promoting long-chain omega-3 fatty acids, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. Replacing the traditional finite marine ingredients, fishmeal and fish oil, in farmed salmon diets with sustainable alternatives of terrestrial origin, devoid of EPA and DHA, presents a significant challenge for the aquaculture industry.
Levels of beneficial omega-3 oils in farmed salmon have fallen significantly in the past five years, a study shows.
BBC News has learned that, on average, levels of omega-3s halved in the fish over that period. Despite this, the analysis shows that farmed salmon is still one of the richest sources of these fatty acids. But the industry is exploring new ways to arrest the decline – which appears to be due to the type of feed given to the farmed fish.
The decline is a result of the industry having to cut back on the amount of anchovies it uses in feed because, previously, it was recognised that far too many anchovies were being caught for fish food.
There has also been a growing demand for farmed salmon across the world. According to Dr Paul Morris, of Marine Harvest, one of the world’s largest producers of farmed salmon, a much reduced supply of fish oil for feed has had to be spread ever thinner.
“We have a fixed amount of fish oil, and we are making sure that we are using that as efficiently as possible. That won’t get us further than a certain amount of the way, so ultimately we will have to look at other sources of (beneficial) omega-3,” he said.
One solution the industry is looking at is to produce fish oils using marine algae, which is how it is produced in the sea.
In the marine environment, microalgae are the primary producers of n-3 LC-PUFA that are subsequently consumed and accumulated through the food chain to give the high levels of EPA and DHA that we generally find in marine, especially oily, fish. Therefore, microalgae represent potential feedstock for food and feed. Indeed,
algal products are already used in human nutrition, particularly in the infant formula market, with 75% of the production volume used in the health food market as dietary supplements. Accordingly, microalgae have been investigated as a promising alternative to the traditional marine derived ingredients in fish feeds, although these have largely been limited to DHA-producing species. The main production of n-3 LC-PUFA by microalgae has predominantly focussed on heterotrophic species (e.g. Schizochytrium, Crypthecodinium and Ulkena species).
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