Atlantic salmon being vaccinated against furunculosis disease. (Photo: Frank Gregersen, Nofima)
Vaccinating farmed fish proves problematic
Friday, August 26, 2011, 22:30 (GMT + 9)
A doctoral thesis at the Norwegian Institute of Food, Fisheries and Aquaculture Research (Nofima Mat) documents that vaccinating against furunculosis principally hides the beneficial effects of the breeding programme against the same disease. However, selective breeding and vaccinating are both common strategies to prevent disease in salmon farming and, as such, the strategies should be coordinated.
Even though virtually all farmed fish are vaccinated, selective breeding for increased resistance against diseases is based on challenge tests with unvaccinated fish. The aim of the research from Nofima was to study whether the breeding programme should be based on testing vaccinated or unvaccinated fish.
Researcher Tale Marie Karlsson Drangsholt has studied genetic variation in resistance against the disease furunculosis in vaccinated and unvaccinated Atlantic salmon. Salmon were infected with furunculosis in controlled challenge tests.
Drangsholt found that disease resistance in vaccinated fish was controlled to a large extent by other genes than in unvaccinated fish.
“This tells us that we must look at vaccination and selective breeding for increased resistance in context,” says Drangsholt.
“Today’s breeding strategy of testing unvaccinated fish is optimal if the long-term goal is a reduced need for vaccination,” says Drangsholt.
In the short-term the optimal strategy is selection based on vaccinated fish, as all fish in the salmon industry are vaccinated.
However, in practice this is not a particularly relevant strategy for furunculosis as today’s vaccine against furunculosis is extremely effective, with extremely few outbreaks in the field. As such, the vaccine hides the beneficial effects of the breeding programme.
Drangsholt also studied whether breeding for increased resistance against disease can also contribute to increasing the negative side effects of vaccinating. Vaccine injuries occur as adhesions in the abdominal cavity and melanin deposits in the organs and on the abdominal wall.
The result pointed to the fact that how easily the fish suffers vaccine-induced injuries is heritable. Therefore the severity of these side effects can be reduced through selective breeding, but the result suggests that it is probably more efficient to obtain this through improvement of the vaccines.
The adhesions and melanin deposits do not appear to have any genetic association with disease resistance against furunculosis, meaning that selection for increased resistance to furunculosis will not result in an unfavourable correlated response in vaccine injuries.
Furunculosis was chosen as the model disease in the research since there is an effective and well studied vaccine against the disease. The challenge tests were carried out on 150 salmon families from SalmoBreed’s breeding stock, and using vaccines from Pharmaq.
Tale Marie Karlsson Drangsholt presented her doctoral thesis at the Norwegian University of Life Sciences (UMB) in Ås. The title of her thesis is “Quantitative genetics of traits related to disease resistance and effects of vaccination in Atlantic salmon (Salmo salar).” Her supervisors are Bjarne Gjerde and Jørgen Ødegård at Nofima/UMB.
The research is financed by the Research Council of Norway and the Fishery and Aquaculture Industry Research Fund (FHF).