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HAVBRUK2-Stort program for havbruksforskning

Serotonin as a welfare indicator in farmed salmon: Role in non-specific mortality

Alternative title: Forskning på uspesifikke dødeligheten: Serotonin som velferdsindikator i laksefisk industrien.

Awarded: NOK 2.2 mill.

Non-specific mortality of salmon constitutes a significant economic and ethical problem in the aquaculture industry. In the current project we have studied a group of fish that contributes significantly to such mortality, the so-called runts. Runts constitute a highly variable (typically 2-20%) but often substantial fraction of fish that die after transfer to seawater. They are anorectic, have stunted growth, and often swim passively in the periphery of the sea cage head up and tail down. In previous work, we have shown that these fish suffer from a long term and health-compromising stress response. Despite the current focus on robustness of fish in aquaculture, potential causes and biological mechanisms behind this syndrome remain virtually unknown. The main aim of this project is to study the interplay between the fish's nervous system and how chronic stress affects behavior, growth and mortality in aquaculture salmon. The main hypothesis is that individual responses to stress can lead to pathology in sensitive individuals. We found that there is a higher amount of runts in freshwater after fish experienced chronic stress in the form of increased CO2 levels, in all families. Physiological systems associated with chronic stress, serotonin and cortisol, were used to establish the runt profile and we have analyzed changes in gene expression of signaling molecules in the brain to understand mechanisms regulating the runt profile. In addition, we found that by manipulating the serotonergic system it is possible to change the runts physiological stress responses, but without reversing their behavioral profile. An interesting result is that it appears that the runt profile may be reversed by changing the social and structural environment. That is, by moving runts into smaller groups and smaller tanks, they exhibit normal growth and behavior. Understanding biological mechanisms that lead to the occurrence of runts will help reduce their occurrence and hence decrease mortality in farmed fish, thus furthering sustainable development of the aquaculture industry.

Vi har funnet at taper fisk kan utvikle seg allerede i ferskvannsfasen på grun av kronisk stress. Dette burde føre til tiltaker som minsker stress allerede i ferskvann. Vi prøver å etablere markører som kan brukes som tildig indikatorer for utviklingen av taper fisk. Dette vil hjelpe å unngå taper tidlig i produksjon.

Non-specific mortality of salmon constitutes a significant economic and ethical problem in the aquaculture industry. The current project will target growth-stunted (GS) fish, a highly variable (typically 2-20%) fraction of drop-outs which display behavioral abnormalities, reduced feeding, stunted growth, and pathological stress responses after transfer to seawater. Despite the current focus on increased robustness of aquaculture fish, production causes and biological mechanisms behind this syndrome remain virtually unknown. Recent studies suggest a gene x environment interaction that can be traced to different families. We will utilize material from an on-going genetic study aiming to increase the robustness of farmed salmon (the NEWCOPE project), but focus specifically on understanding mechanisms leading to the GS phenotype. Target families (established in the NEWCOPE project) showing differences in susceptibility to developing the GS phenotype will be sampled at fresh- and seawater stages. we believe that a combination between immune and stress challenges are behind the GS phenotype. Therefore, blood and brain samples will be analyzed before and after vaccination and after seawater transfer, in order to characterize coping physiological markers (focusing on serotonin neurochemistry and immune activation) characterizing GS fish. Cognitive function associated with healthy physiological responses will also be assessed before and after vaccination. In this way, physiological markers will be established as indicators for the GS phenotype (WP1). Finally, the serotonin system will be manipulated in order to induce and reverse the GS phenotype, in order to establish its direct role in regulating this phenotype (WP2). In summary, this project will ascertain the mechanism regulating the GS phenotype and contribute to reduce non-specific mortality in aquaculture, thus furthering sustainable development of the aquaculture industry.

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning