The feedstuffs contain some vitamins and minerals and the fish also gets a mineral intake from the water. However, in order to cover the fish's needs, vitamins and minerals are added to the feed.
In recent times, scientists have started to focus on whether compounds such as nucleic acid (as DNA) can also have a nutritional significance. In addition, there are immunostimulants or in other words compounds that influence and strengthen the fish's immune defence, and so-called prebiotics, which promote a favourable gut flora.
Vitamins and minerals
Requirements for each vitamin and mineral are unique for each species, and these requirements vary with size and development stage. Scientists at Nofima are working on areas including what significance minerals in the feed have on bone formation right from first feeding.
By individually tagging the fish and taking new images as the fish grows, we can follow the individual fish's skeletal development. Such studies have shown that the zinc and phosphorus content in the feed at an early stage is extremely important for the bone mineralisation. Small fish are particularly sensitive to the lack of these nutrients, and even marginal shortages, which results in a deficit over time, can lead to skeletal deformities.
Carotenoids
The red colour of the fillet is an extremely important quality parameter for salmonids, with consumer surveys showing that only freshness is rated as more important. The fillet colour of salmonids is attributed to salmonids' unique ability to deposit relatively large amounts of compound called carotenoids in the muscle. Fish do not produce these compounds naturally and, for this reason, it is added to the feed of farmed fish.
The aquaculture industry in Norway today mainly uses the carotinoid astaxanthin, which is manufactured using synthetic chemicals. Astaxanthin also occurs naturally in wild salmonids. The manufacture of astaxanthin is an expensive process and the utilisation rate in Atlantic salmon is also relatively low. Less than 15 percent of that consumed by the fish remains in the fish's musculature. An important reason for this is that astaxanthin is not particularly soluble in water and has a poor absorption rate from the intestine.
The digestibility (the proportion of the consumed amount that is absorbed from the intestine) is normally around 50 percent reliant on the dose and fat content in the feed. We recently proved that digestibility may also be influenced by temperature and feed intake and that it varies in the course of the production cycle.
Further description
