Occurrence of pigment spots and stress response in salmonid fish

Janne Karin Brodin

The occurrence of pigment spots – dots on the skin of salmonid fish – is an indicator of stress response in the fish. This is one of the conclusions of PhD student Silje Kittilsen’s doctoral thesis.

Fish farming is an intensive production system and can be stressful for the fish. Salmonid fish make up the main part of Norwegian fish farming. In salmonid fish, sensitivity to stress varies a great deal between individuals within a species, and is an inherited trait / characteristic. Breeding fish that are more resistant to stress may therefore be beneficial in many ways, and will be an important tool in reducing health and welfare related problems in farmed fish. In this doctoral work, variations in stress sensitivity and the accompanying traits / characteristics have been investigated.

Silje Kittilsen Photo: Janne Brodin

Black spots and salmon lice
Individuals that differ from each other in cortisol response – i.e. that are different as regards sensitivity to stress – show variations in behavior. However, the more remarkable finding is that the cortisol response in salmon and trout is associated with the black spots on the skin (made by the pigment melanin) that are so typical in salmonid fish. Fish that have many spots display a lower cortisol response (stress response) when exposed to stress. The number of spots varies significantly also within domesticated populations, and the most interesting fact is that the spot pattern seems to coincide with resistance to the parasite salmon lice. It seems that salmon lice develop slower on fish that have a lot of pigment (pigment spots) on their skin.

Laks Photo: marxus SXC

Breeding
The background for this doctoral work is the need for improving animal welfare through a greater understanding of the connection between various factors affecting sensitivity to stress in salmonid fish. The results may be important to fish breeding in order to reduce susceptibility to stress in salmonid fish.

Silje Kittilsen is 33 years old, and comes from Kviteseid in Telemark, Norway. She took her Cand. scient degree at IHA in 2004. The trail lecture and public defence took place December 4 2009 at IHA

Title of the thesis: Stress Responsiveness in Salmonid fish: The Cortisol Response and Associated traits. Prescribed subject of the trail lecture: Functional aspects of emotions in fish.

Professor Bjarne Braastad has been main supervisor. and Dr. Øyvind Øverli has been assistant supervisor.

Published: 07.12.09
Updated: 08.12.09
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