Salmon Can Have a Firmer Fillet

The firmness of salmon fillet is something the consumer perceives as a characteristic of quality and is an important factor for processing by the producer. By making use of new gene technology methods in quality research, Larssons PhD project points to the fact that the key to a firmer fillet lies in efficient metabolism of nutrients in the cells, and that this is determined by the genes in the fish.

In order to find the biological difference in salmon with soft and firm fillet, we have used a method called microarray. This is a method used to study if genes are turned on or off in salmon with varying firmness in their musculature, says Mr Larsson.

Gene analyses tell us what happens in the fish at a molecular level and indicates the cause of undesirable softness in the fillet of farmed salmon. By studying thousands of genes simultaneously, the method functions as an efficient screening tool to point to key factors that influence the firmness.

The microarray used here is specific for salmon and was developed at Nofima by Aleksei Krasnov. This is a suitable method for studying regulation of genes in salmon. This new approach regarding the use of method in Mr Larssons work made it possible for the first time to map the biological causes of variation in the firmness of salmon fillet.

Efficient conversion of nutrients occurs in the cellular energy plants, the mitochondria (aerobic metabolism). The gene analyses showed that salmon with firm fillet had more aerobic metabolism, by using fat as fuel, than salmon with softer fillet. Efficient mitochondria were a requirement for the formation of firmer salmon fillet.

The knowledge from the gene analyses was used as a basis to design salmon feed that stimulates formation of firmer fillet. A feeding trial involved salmon feed with extra amino acid supplements (glutamate) being fed to one group of salmon, while another group received normal feed. The salmon that received the feed containing extra glutamate had stimulated aerobic metabolism, which resulted in a firmer fillet. Positive health benefits were also observed. Sick salmon are not in a position to fulfil the biological requirements to form normal firm muscle, and these fish instead developed abnormally hard muscle.

Thomas Larsson is 31 years old and comes from Lysekil in Sweden. He presented his PhD thesis at the Department of Animal and Aquacultural Sciences (IHA) at the Norwegian University of Life Sciences in s on 12 November. The title of his PhD thesis is Molecular basis of fillet firmness in Atlantic salmon (Salmo salar L.). The main supervisor is Turid Mrkre, IHA /Nofima. The Research Council of Norway, the Norwegian Seafood Research Fund (FHF) and Nofima have made financial contributions to the PhD project.