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HAVBRUK2-Stort program for havbruksforskning

Optimising dietary fatty acids and lipids of Atlantic salmon to secure their health and welfare through varying environmental conditions

Awarded: NOK 2.2 mill.

This post-doc has been connected to the FHF funded project EPA-salmon (project number 901282) focusing on an important challenge in the Norwegian aquaculture sector; the lack of fish oil for aquafeeds for a sustainable growth in the production of healthy salmon. Since fat and specific fatty acids have central roles in many biological functions, changes in the feed?s fat composition can affect the fish growth, development and health. The Optihealth project focuses on the areas where knowledge is lacking concerning the requirements for omega-3 fatty acids. This includes the interactions with total fat levels and omega-6 fatty acids in the feed and the effect on the health of the salmon, especially under challenging environmental conditions. The typical marine fatty acids, EPA and DHA, are important for both the salmon and for people. With a limited availability of these fatty acids from fish oil, it is important to optimize the way we utilize them. When you feed the salmon with these fatty acids, some of them will be used as an energy source. The goal is to make the salmon use other fatty acids for energy, maximizing the tissue storage of EPA and DHA, as well as securing their availability for essential metabolic processes in the fish. This post doc has focused on parts of the main project Optihealth as described below. The remaining work will be reported in the main project Optihealth. -Feeding trial in sea with varying EPA and DHA content Salmon from ~200g to ~5kg were given feed with EPA and DHA levels at 10, 13, 16 and 35 g/kg and fat levels at usual commercial levels for each size of the fish. In addition, a fourth diet was used, with half the fat content of the other feeds, and an EPA and DHA content at 13 g/kg. After a delousing, fish were sampled to investigate how different levels of EPA and DHA affect the stress handling of the fish. Plasma cortisol clearly showed that the fish had been stressed, but the response was the same in all dietary groups. There are analyses pending in this part of the project. -Growth trial with varying dietary n-6/n-3 ratios In a feeding trial with salmon in land-tanks (fish weight 80g-800g) we have the fish feeds with varying ratio between n-6 and n-3 fatty acids (n-6/n-3 ratios at 1,2 and 6). These three diets all had the same amount of total n-3 and sum of EPA and DHA, but with an increasing amount of n-6 to increase the ratio of n-6/n-3. We also had an extra dietary group which also got a feed with an n-6/n-3 ratio at 1, but with twice the amount of each of the two groups of fatty acids as the other feed with the same n-6/n-3 ratio. The hypothesis was that the requirement of the important fatty acids EPA and DHA could be affected by the ratio of n-6/n-3 fatty acids in the feed, and that also the total amount of these fatty acids might affect the use of EPA and DHA. The growth was not affected by an increased n-6/n-3 ratio, but the fish given the feed with a higher EPA and DHA content had a higher final weight. We saw no differences between the groups in mortality or health issues. One of the conclusions from this feeding trial was that it appears that the fish uses the essential marine fatty acids more efficiently (i.e. a higher percentage of the eaten fatty acids are stored) when the dietary n-6 is kept low. It might therefore be possible to have a more efficient use of EPA and DHA by keeping the n-6 in the feeds low. Fish given these same diets were also used in the two last trials described (stress- and gill health trials). -Stress trial with varying dietary n-6/n-3 ratios Fish given the same diets as described above, were used in a stress trial. Fish were distributed in different tanks and some of the tanks were subjected to repeated chronic stress (reduced oxygen levels) for six weeks. Before the last sampling, all fish were subjected to an acute stress (handling stress). With this trial design we could gain knowledge not only on the effects of diets on the fish's ability to handle stress, but also say something about whether the fish that had been exposed to a chronic stress would handle an acute stressor differently from fish that hadn't been stressed through this period. Results still need to be processed. -Gill disease in fish given varying dietary n-6/n-3 ratios The third trial with fish given the diets with varying n-6/n-3 ratios were exposed to a gill infection (AGD). AGD is a gill disease caused by an amoeba (Paramoeba perurans), which reduces fish health by attaching to the gill arches and leading to a lowered respiratory capacity and reduced appetite. An interesting finding here was that the group fed a diet with an n-6/n-3 ratio at 6 grew less than the other dietary groups after AGD infection. This might indicate that this group were less resilient towards this specific combination of disease and repeated stressors with weekly samples (since this group did not grow less in the growth trial). Some analytical work remains in this part.

Dette post doc prosjektet har bidratt med viktig kunnskap om effektiv bruk av marine fettsyrer og har vært en stor del av arbeidskraften lagt inn i optihealth prosjektet.

The proposed project aims to generate new knowledge regarding dietary fatty acid and lipids for Atlantic salmon to secure fish health and welfare through challenging environmental conditions and different life stages. Due to shortage of fish oil, such knowledge is necessary for sustainable growth of the salmon industry while securing fish health. To solve this challenge, a unique project consortium has been assembled, including the three major players within research on lipid nutrition in salmonids in Europe (Nofima, Nifes, University of Stirling), two of the major feed companies (Biomar, Skretting), as well as partners with particular expertise in the areas of immunology, gill infections and neuroendocrine stress response (UiO, NIVA, Uppsala University). In this project, EPA and DHA requirements during long-term growth in sea cages will be fine-tuned in the area between 10-16 g/kg of the diet, where knowledge is currently lacking. The potential impact of lipid level on the requirement will be studied. Shorter term land-based trials will distinguish the health effects of the level of n-6 fatty acids from the n-6/n-3 ratio and the n-3 level, as well as give information about the effects of the different n-3 fatty acids (EPA, DHA and ALA) alone, in combination and in different ratios. Furthermore, the impact of genetic background and life stage of the fish will be studied. All trials will include assessment of the retention and deposition of EPA and DHA in whole fish and different tissues, as well as evaluation of health status and study of lipid metabolism. Additionally, as the dietary fatty acid composition needs to be adequate for fish exposed to the various challenges in commercial aquaculture productions, our land-based trials will include tests of how the fish cope with hypoxia/ chronic and acute stress, a gill infection challenge and vaccination with subsequent evaluation of immune responses.

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning