Functional feeds – tomorrow’s feed for farmed salmon

Professor Kjell-Arne Rørvik (English translation: Ane Skjelfjord)

Efficient breeding and access to feeds rich in energy have caused problems for the breeding industry in that salmon may mature as early as after 1.5 years in the sea. In her doctoral studies, PhD student Henriette Alne has concluded that adding the fatty acid tetradecylthioacetic acid to the feed reduces the problem of early maturation.

Henriette Alne Photo: Janne Brodin

Low first year performance in the ocean
In an introductory study, Alne shows that farmed salmon goes through a stage during the first year in the ocean that is characterised by reduced appetite, feed utilisation, growth and fat content. This happens whether the fish is put out in spring or in autumn. Furthermore, it seems that these low performance periods may set off the outbreak of illness.

Adding fatty acid increases metabolism
In her doctoral work, Henriette Alne has studied the use of tetradecylthioacetic acid (TTA) in feeds used for salmon in the ocean. TTA is a fatty acid which in chemical terms resembles an average fatty acid, but which has a particular metabolic effect. Given at the right time and in the right dosage, it has been shown that TTA increases the salmon’s capacity to metabolise fat (mitochondrial β‑oxidation) in the muscle, and doubles the activity (expression) of genes involved in fat metabolism in the heart.

The problem of early maturation
Salmon’s natural generation span is of 4 years, and in its natural state, it matures after 2.5 years in the ocean. In recent years, access to energy rich feeds in the breeding industry led to the problem of salmon maturing after 1.5 years in the ocean. Efficient breeding and even more efficient feeds now appear to induce increased maturation as early as during the first autumn the fish spends in the ocean (only male fish and clearly most relevant for autumn smolt after appr. 12 months in the ocean). If, and when, salmon matures depends partly on the energy status of the fish in spring – i.e. several months before maturation. Adding TTA to the feed during the first spring in the ocean turned out to reduce the fat content in the fish. This reduced the problem of early maturation with as much as one third for spring released smolt.

Reduced mortality and stress
In the TTA experiments, salmon smolt put out in the ocean in spring had a natural outbreak of the viral infection Infectious Pancreatic Necrosis (IPN), whereas smolt put out in autumn contracted Heart and Skeletal Muscle Inflammation (HSMB) during their first spring in the ocean. Adding TTA to the feed reduced mortality from IPN to 1/3 (from 7.8% to 2.3%), whereas mortality from HSMB was halved (from 4.7% to 2.5%). The work done for this thesis does not reveal the direct causality of the increased survival rate. However, for IPN it was shown that TTA led to improved adaptation to sea water during the weeks after release into the ocean (reduced osmotic stress), and an up regulation of genes involved in fat metabolism in the heart was shown during the outbreak of HSMB.

At the forefront of feed development
As an industrial research centre Nofima has been at the forefront of the development and improvement of feeds for the fish farming industry. Recently, the focus has been on adjusting the feed to the salmon’s biological rhythm during the ocean phase of production. Developing these new functional feeds presupposes extensive knowledge on the natural environmental variations throughout the year, and the salmon’s reaction to them. In this doctoral thesis, Henriette Alne points to the importance of developing functional fish feed ingredients for modern fish farming, in order to gain better control of growth, reduce the percentage of early maturation and improving resistance to viral infections.

A Marine Harvest employee
Henriette Alne is 27 years of age, and originally a native of Ølensvåg in Rogaland. She has a Master’s degree of Aquaculture with nutrition and economics as focus areas, from the Norwegian University of Life Sciences (UMB) at Ås. She started her doctoral work at UMB and Nofima in 2006. Her supervisors have been professor Kjell-Arne Rørvik and professor Magny Thomassen of Nofima Marin / UMB.

Today, Henriette Alne is employed as a feed coordinator in the world’s largest fish farming company, Marine Harvest.

She will defend her thesis at IHA on Friday May 28th 2010, at 12:15 hrs.
The title of her thesis is “Functional feed for Atlantic salmon (Salmo salar L.): Impact of tetradecylthioacetic acid (TTA) on health, sexual maturation and growth performance”.

Her trial lecture will be on Development of fish feed formulation in light of economical and biological sustainability.

The committee members are Dr. Rodney Wootten, University of Stirling in Scotland and editor of the scientific journal “Journal of Fish Diseases”, Professor Dr. Sigurd Stefansson, University of Bergen, Dr. Jon Arnason Matis, Iceland and Professor Dr. Ragnar Salte, UMB

Updated: 25.02.11
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