Negative genetic correlation between resistance against Piscirickettsia salmonis and harvest weight in coho salmon (Oncorhynchus kisutch)

• We evaluated genetic co-variation for P. salmonis resistance and harvest weight.
• Heritability for P. salmonis resistance was 0.16 ± 0.04.
• Heritability for harvest weight was 0.41 ± 0.03.
• Genetic correlation between these traits was − 0.50 ± 0.13.

One of the major infectious diseases affecting coho salmon (Oncorhynchus kisutch) aquaculture is the Salmon Rickettsial Syndrome caused by Piscirickettsia salmonis. Conventional control measures such as antibiotics and vaccines have shown inconsistent results in production conditions. Thus, genetic improvement for P. salmonis resistance represents an alternative for the prevention of outbreaks. In the present study we aimed to determine both the levels of genetic variation for P. salmonis resistance (PSR) and genetic co-variation between PSR and harvest weight (HW) in coho salmon. A total of 2606 siblings from 108 maternal full-sib families (60 paternal half-sib families) were challenged against P. salmonis. The cumulative mortality rates among families ranged from 5% to 82%, with an average of 39%, indicating considerable phenotypic variation. For the genetic analyses PSR was defined as the day of death for each fish. We also recorded HW in 41,597 genetically related individuals of the challenged fish from the same breeding population. A linear bivariate animal model was used to estimate (co)variance components and to calculate genetic parameters. Estimated heritabilities for PSR and HW were 0.16 ± 0.04 and 0.41 ± 0.03, respectively. The genetic correlation between PSR and HW was − 0.50 ± 0.13. The levels of genetic variation detected in the present study indicate that selective breeding for these traits is feasible. However, the magnitude and direction of the genetic correlation between PSR and HW must be taken into account when selecting both traits simultaneously.Statement of relevanceNegative relationship between resistance and growth in coho.