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NAERINGSPH-Nærings-phd

Dietary modulation of salmonid skin defences

Alternative title: null

Awarded: NOK 1.4 mill.

Project Manager:

Project Number:

232050

Project Period:

2013 - 2017

Funding received from:

Partner countries:

The project has now finished. The overall aim of the project was to investigate how functional ingredients in fish feeds might modulate the natural defences in fish skin, to enhance protection towards sea lice. Firstly, a novel in vitro bioassay was developed to investigate if functional ingredients may modulate salmon kairomones (?smell?)to make them less attractive to sea lice. Secondly, salmon and trout mucus biochemistry (viscosity, protein and carbohydrate concentrations, and enzymatic activity) was investigated, and lastly, 2 in vivo trials were conducted to assess the impact of functional ingredients on the gene expression of salmon and trout skin. During this project it was found that functional ingredients in fish feed can modulate the smell of Atlantic salmon to reduce the attraction of sea lice, and modulate the expression of immune genes in the skin, although the gene expression profiles differ depending on the fish species and distance to the louse attachment site. Therefore, this project showed that functional ingredients in fish feeds can be used to modulate various aspects of fish skin and so, this project has provided further evidence that functional fish feeds can be a useful tool in the fight against sea lice infections in fish farms, whilst at the same time being more natural, sustainable, and less stressful for fish. NB: Due to the sensitive nature of the results, Skretting ARC has placed a 5 year embargo on the publication of the thesis, however paper publications are expected in due course

Ultimately this PhD aims to identify a functional ingredient(s) that can be used in a new feed formulation for Skretting to reduce sea lice burdens on Atlantic salmon as part of integrated past management. In doing this, understanding of salmonid skin def ences, how they can be modulated through diet and the host parasite relationship will also be furthered. The methodologies for screening microingredients will be compared, validated, refined and made as high-throughput and quantitative as possible. The ba ckground for this study is 1) sea lice are a major pest and threat to Norwegian salmon farms, 2) there is known interplay between nutrition, the immune system and susceptibility to infection, 3) nutritional modulation of host defences has previously been shown to enhance protection in fish species to various pathogens and 4) other salmonids show resistance to sea lice. This suggests that incorporating certain ingredients into salmonid feeds can potentially enhance Atlantic salmon resistance to sea lice. This PhD will concentrate on the host defences and modulation of the skin as this is the site of lice infection and first point of contact. Several phases to this PhD have been proposed. Initial phases involve screening and selecting microingredients by a ssessing, in vitro, lice predilection. Subsequent phases will then assess the effects of selected microingredients on salmonid skin mucus and epidermal parameters. The final phases involve sea lice-salmon challenge trials in which the effectiveness of sel ected microingredients to reduce sea lice burdens will be tested, as will the differences in susceptibility of different populations of salmon. It is expected that methodologies such as immunohistochemistry, proteomics, histology and genetics will be util ised. Regular visits to the University of Aberdeen will be made for courses, assessments, presentations/seminars and use of laboratory equipment. This PhD works towards more natural and sustainable farming.

Funding scheme:

NAERINGSPH-Nærings-phd