Farmed salmon frequently suffer from poor health. According to Norwegian Directory of Fisheries statistics, one out of every five salmon never get as far as the slaughtering table. The changed composition of salmon feed is probably one of several causes of this: Salmon are getting less and less marine material in their feed, because the availability of fish-meal and marine oils cannot keep up with the growth in production in the aquaculture industry.
A recent NIFES study has shown that adding extra arginine, an essential amino acid, to feed, can increase breakdown of fat in liver of salmon.
“We assume that leaner farmed salmon are healthier, which will also give reduced losses at slaughter,” says research associate Synne M. Andersen of NIFES.
Both fish-meal and many types of plant protein have high levels of arginine, so this is not a matter of adding arginine in order to meet the nutritional requirements of salmon, but rather of adding a little extra to make the fish more robust and perhaps more resistant to infectious diseases.
As a background to the study, Ms Andersen and her colleagues carried out feeding trials, in which salmon were fed diets based on commercial feeds, mainly based on plant protein. These diets were then supplemented with higher levels of arginine than what have been established as a requirement for growth in salmon.
As well as being a protein building block, arginine affects a number of metabolic processes, including gene expression (how genes operate within cells), the release of hormones and the production of polyamines, which are essential for cell growth. The research team found that polyamine metabolism in the livers of the fish increased, an indication of stronger cell growth.
Experimental research on mammals has already demonstrated that adding arginine to feed can reduce intestinal fat and help to build up muscle. The research team now wants to look more closely at whether extra arginine actually does add muscle and reduce visceral fat in salmon too.
“In our study, we did not find a clear effect on patterns of fat storage and muscle growth. However, fat metabolism in the liver did increase which can lead to less visceral storage of fat and possibly a healthier fish. The next stage in our research will be to look at the molecular mechanisms involved in order to find out more about the relationship between arginine and growth and health of salmon,” says Ms Andersen.
The study has been published in the British Journal of Nutrition. It was financed by Ewos Innovation and the Research Council of Norway and carried out in collaboration with the University of Bergen and Evonik Degussa Corp.