Koi herpes virus resistance in carp can be improved

The common carp is the third most important farmed fish species in the world. However, serious diseases such as Koi herpes virus (KHV) threaten farming in many countries. Nofima and their partners in the EU project EUROCARP have found that this disease is highly heritable and can be effectively fought by selective breeding.

This was found when the researchers crossed individuals of four common carp strains of wild and cultured origin, and tested their survival after KHV infection. For each family, 20 individuals were tested. The 91 families that were tested showed very large variation in survival after infection.

High survival in some families

The survival rates of the purebred strains and their crosses varied between 0 and 8 % after testing. In spite of the low variation between strains and crosses, there was a large genetic variation within strains and crosses. Out of the 91 families tested, 60 were completely wiped out by the disease, but there were families showing up to 45 % survival.

Dr Jørgen Ødegård, researcher in Nofima (Food, Fisheries and Aquaculture Research Norway), says that although there was a high overall mortality, there are good reasons for optimism: “The large variation between families shows that the genetics of common carp is crucial for the resistance against KHV, and our research shows that 80 % of the variation in resistance to this disease is due to different genes of the individual. This means that by applying a selective breeding program, where reproduction of the resistant families and individuals is facilitated, one could efficiently improve KHV resistance in common carp considerably within few generations”.

Genetic tools not implemented yet

At the moment, selective breeding programs for carps are limited, unlike some other major aquaculture species such as tilapia, shrimp and salmon. Common carp is produced in both Asia and Europe, and KHV is present in both continents. The research group in the EUROCARP project strongly recommends that a large scale selective breeding programme involving KHV resistance and other important traits (e.g. growth and survival) should be considered.

The project is funded by EU and is coordinated by the Hungarian HAKI (Research Institute of Fisheries Aquaculture and Irrigation). In the project group, the British CEFAS (Centre for Environment, Fisheries and Aquaculture Sciences) was responsible for the challenge testing with KHV in this study. The study was presented by Jørgen Ødegård at Aquaculture Europe recently.