By Bente Torstensen
As long as the nutritional requirements of salmon are met, it is of little importance what ingredients are used. To put it simply: salmon need nutrients, not just ingredients.
As is the case for us humans, fish must meet their nutritional requirements by eating fat, proteins, carbohydrates, vitamins and minerals every day. We get the nutrients we need by eating a varied diet as recommended by the Norwegian Directorate of Health. Farmed salmon get the nutrients they need from fish feed made from fat and protein ingredients, to which the necessary vitamins, minerals and other essential nutrients are added, as well as a starch to bind it all together into feed pellets.
Though it is controversial for humans to eat a low-carb diet, this is not the case for salmon. Salmon is a carnivorous species, a predatory fish, which eats fish and crustaceans in the wild. This means that they need to eat a lot of protein and fat to grow well and be healthy, while they tolerate very low levels of carbohydrates in their diet.
Fifteen years ago, salmon feed was made from fish oil and fishmeal, which are very good sources of fat and protein. The marine ingredients, fish oil and fishmeal, were made to utilise the fish resources that couldn’t be used for human food and were previously used as fuel and for agricultural livestock feed. They were cheap, easily available and gave the fish plenty of marine fat, high quality protein and an abundance of vitamins and minerals. Today, fish oil and fishmeal are a limited and valuable resource, which is why pellets with more ingredients from the plant kingdom are now being used, and have been increasingly so over the last decade.
Vitamins and minerals that the fish previously got from the marine ingredients can be produced and added to the feed in the quantity required by the fish. New research shows that more of several types of minerals and vitamins must be added to feed based on plant ingredients in order to meet the nutritional requirements of salmon and to ensure good growth and the production of robust fish. This is because the composition of ingredients and the chemical form of the nutrients are crucial in determining the amount of nutrients that are needed to meet the salmon’s requirements.
Many of the components in feed affect how effectively vitamins and minerals are absorbed and utilised by the salmon. For example, fishmeal is a good source of the mineral selenium, because, among other things, the selenium in fishmeal is the form that is most easily absorbed and utilised. If all the selenium is added in a different chemical form, lower bioavailability of selenium must be compensated for by adding more to meet the salmon’s requirements. Other components in plant ingredients, such as fibre and phytate can reduce the bioavailability of the minerals zinc and manganese for the salmon. In this way, the composition of ingredients is decisive for how much nutrients the feed must contain in order to meet the salmon’s practical nutritional requirements.
Salmon require nutrients, but the fat and protein ingredients determine the salmon’s practical nutritional requirements in the fish feed of the present and of the future.
Printed in the newspaper FiskeribladetFiskaren, 26 November 2014.