Plant ingredients contain many of the essential nutrients farmed fish need, but not all of the nutrients that fishmeal and fish oils previously supplied an abundance of. Vegetable oils do not contain long-chain omega-3 fatty acids, EPA and DHA, and nor do they contain enough of certain essential amino acids such as histidine and methionine.
Should limit the use of omega-6 fatty acids
Salmon ‘are what they eat’ with respect to certain nutrients, but not all of them. One example of a nutrient where salmon ‘are what they eat’ is omega-6. Certain vegetable oils, such as soya oil and sunflower oil, are very rich in the omega-6 fatty acid linoleic acid (18:2n-6).
The intake of omega-6 is generally too high in Western diets, and the use of omega-6 should be limited in the production of food. This also applies to farmed salmon, so that it does not also become a food that adds too much omega-6 to our diet.
Norwegian farmed salmon is a moderate source of omega-6. To ensure that salmon remains a moderate source, the use of omega-6 in fish feed should be limited in the further development of feed for farmed salmon.
Salmon itself produces marine omega-3
The content of marine omega-3 fatty acids decreases when salmon are fed with vegetable ingredients. However, salmon is still a very good source of marine omega-3 in our diet. Farmed salmon today contain enough marine omega-3 that one portion of salmon covers one week’s recommended intake for healthy people.
Farmed salmon that are fed low levels of marine omega-3 through their diet compensate by producing it themselves from plant omega-3 from vegetable oils. When plant omega-3 fatty acids are added to the feed, the salmon produce marine omega-3 themselves, and this system is more effective when the salmon are fed low levels of marine omega-3.
We know that salmon have a minimum requirement for marine omega-3, but we still don’t know how little is enough to ensure that the salmon are healthy, grow well and have good fish welfare.
Protein in plants
The protein content of plants is very different to that of marine ingredients, and it can also vary a lot from plant to plant. For example, soya beans have a high protein content while maize
At present, fish feed contains between 38 and 45 per cent protein depending on the protein requirement of the fish during the different life phases. Small young fish generally need more protein than bigger adult fish. The protein sources from plants are refined to remove anti-nutrients and indigestible carbohydrates that are not beneficial for the fish.
Amino acids in plant protein
The protein sources that are used in fish feed must cover the fish’s nutritional requirement for essential amino acids. No plant protein contains the correct amount of all the essential amino acids, which is why protein sources from several plants must be mixed together depending on their composition of amino acids. It is also possible to add crystalline amino acid(s) when the raw materials contain too low levels of these to meet the fish’ amino acids requirements.