Quantitative genetics of behavioral responsiveness in Atlantic cod (Gadus morhua L.)

Summary

In selective breeding it is important to understand whether there is genetic variation in behavior as this trait is important for fish welfare and it can possibly be correlated to other production traits. However, behavioral studies in farmed fish are still in their infancy and few automated screening methods have been developed. The aim of this study was to estimate heritability of behavioral responsiveness in farmed Atlantic cod, Gadus morhua L, using automated screening of swimming activity of individual fish. The sampling included 320 fish (offspring of 15 dams and 14 sires) from the Norwegian national cod breeding program. Video recordings of individual fish were taken prior to and after a two minute period of mild stress (rapidly moving light). Observations were made on the percentage of time spent in the central zone of the tank and the swimming speed for each individual. Estimates of heritability for time spent in the central zone both before and after the stress period were intermediate (0.21 ± 0.10 and 0.31 ± 0.13, respectively). Similar estimates of heritability were found for swimming speed before and after the stress period (0.37 ± 0.15 and 0.21 ± 0.11, respectively). The genetic correlation of observed behavior before and after the stress period was strong for both the amount of time spent in the central zone and swimming speed (0.90 ± 0.10 to 0.92 ± 0.11), indicating that families rank similarly before and after the stress period. Results from a challenge test for vibriosis resistance on the same families were made available from the Norwegian national cod breeding program, and revealed slight negative correlations among estimated breeding values for vibriosis resistance and time spent in the central zone before the stress period, as well as for swimming speed before and after the stress period. Thus strong disease resistance may be associated genetically to low behavioral activity and low stress response. The results of this study demonstrate that non-invasive automatic behavioral screening can be used for genetic analyses of behavior related to stress coping mechanisms in fish.