Scientist Jens-Erik Dessen has studied what farmed salmon should eat in order to optimize growth and health.

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Reidun Lilleholt Kraugerud  

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Simplified, fish farmers want to get the most out of their inputs – the fish and feed. However, fish farming is influenced by environmental conditions, operating form, smolt quality and infectious diseases – all of which vary widely.

This was the starting point for Jens-Erik Dessen’s PhD work, under the supervision of Professor Kjell-Arne Rørvik, which included trials in pens in three very different farming locations along the Norwegian coast. Dessen will defend his doctoral work 12 December.

How protein and fat affects growth

“The experiments lasted up to a year and a half, in order to identify important connections, giving us unique insight into how variables in the environment, feed and fish affect the production,” says Dessen.

He has studied at how the protein and fat content in the feed affects growth, feed utilization, health, quality and fat deposition in farmed salmon. This was done to identify good balances in the dietary protein-to-lipid ratio related to different seasons and periods with high risk of viral diseases (pancreas disease).

Three recommendations

He has performed four studies in his PhD and has three general recommendations:

‒ Smolt transferred to sea in spring require high dietary energy and high protein content during the early seawater phase for optimal growth performance.

‒ Increased dietary protein-to-lipid ratio could be utilized during the first spring and summer in sea for sites with high risk of pancreas disease outbreaks to improve survival and reduce the accumulation of severely thin diseased fish (runts).

‒ High fat content in the fish, especially in early autumn, reduces the long-term growth potential.

Jens-Erik Dessen has also investigated if there has been significant effects of the different feeds on fillet quality, such as firmness, gaping and color. There wasn’t. Photo: Joe Urrutia © Nofima.

The trials were performed in small-scale at Averøy Research Station and in large-scale at Nofima’s research facilities in southern, central and northern Norway. This was done in order to ensure research that could be of practical relevance for the fish farming industry.

Nofima’s partners in these trials have been Blom fiskeoppdrett AS, Nordlaks oppdrett AS, Lerøy Midt and BioMar. The research is mainly funded by Nofima, while the small-scale trials were partly funded by the Fishery and Aquaculture Industry Research Fund (FHF) and Havsbrún.

About the doctorate

Jens-Erik Dessen is 32 years from Røyken south-east in Norway. He has a Master degree in aquaculture from the Norwegian University of Life Sciences (NMBU) and has worked for six years in Nofima with research in fish nutrition.

Dessen dissertates 12 December at 12:15 at NMBU Ås, with the thesis titled «Growth, feed utilization, health and biometric parameters in Atlantic salmon (Salmo salar L.) – Influence of dietary protein-to-lipid ratio and body fat status».

Theme for the trial lecture is “Novel protein ingredients in salmon feeds – opportunities and threats”.

His supervisors on the doctoral work has been Professor Kjell Arne Rørvik (main supervisor), Professor Magny Thomassen, Professor Turid Mørkøre, Dr. Bjarne Hatlen and Professor Bente Ruyter.


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