Salmon louse can cause prolonged and exhausting stress

Janne Karin Brodin

Salmon louse is a parasite that latches on to the fish and causes prolonged and exhausting stress in farmed salmon. The fish may also be exposed to other stress factors, such as insufficient nourishment, disease and environmental poison.

Stanko Skugor Photo: Janne Brodin

Through looking at, among other things, changes in the genes that are activated from stress (changes in gene expression), PhD student Stanko Skugor has been able to observe the fishes’ response to stress. Changes in gene expression due to salmon louse attack points at a combination of chronic stress, reduced healing ability and changes in the immune response.

In his thesis work, Skugor has concluded that salmon louse attack prompts a complex inflammation process in the fish, something that in its turn leads to delayed healing of skin damage and weakening of the T cell response. T cells are “defence cells” which circulate in the blood and the lymph. Prolonged louse infection may lead to reduced immunity and self-destruction of tissue.

Lakselus Photo: Thomas Bjørkan

Varying effect from vaccines
Skugor’s studies of gene expression also shows that the effect of vaccines depends on the degree to which the fish can tolerate the vaccine – i.e. the ability of the fish to neutralize the negative effect of the immune response, combined with the efficiency of healing of tissue damage.

Changing the feed can cause stress
Changes in feed components were also shown to lead to changes in the expression of stress related genes, according to how well the fish tolerated and utilized the new feed ingredients. Especially, the fish showed a stress response to feed containing soy.

Growing fast is stressful
Salmon are bred for speedy growth, which is a stress component in itself. There is biological stress within the fish’s body because it undergoes large changes. Stress related genes are expressed more when the fish is at its maximum growth rate.

Immunostimulant
Skugor also participated in a study where a dietary supplement (the mushroom Letinule edodes, or shiitake mushroom) was added to the feed. Immuno stimulants can be beneficial, and the study showed that the supplement reduced the expression of genes related to acute inflammatory responses.

Stanko Skugor is 39 years old and from Belgrade in Serbia. He took his Master degree in Intensive Fish Farming at UMB in 2006. He has been employed at Nofima Mat as PhD student and is now employed at Nofima Marin as Post doc.

Director of Research, Breeding and genetics Nofima Marin and Associated Professor-II at IHA Kari Kolstad and senior scientist Aleksi Krasnov, Nofima have been supervisors for Skugor.

Updated: 09.03.10
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