Inbreeding among cultivated Atlantic cod (Gadus morhua) and its effects on offspring

No abstracts are to be cited without prior reference to the author.

Farmed Atlantic cod (Gadus morhua) spawn in cages, releasing eggs into the environment. With potentially thousands of siblings in a cage, the likelihood of inbreeding during spawning is high. Inbreeding may produce poor‐quality offspring which could mature and interbreed with wild cod, possibly reducing the fitness of farmed–wild cod offspring. The goal of this project was to determine if inbreeding occurs among farmed cod, and if inbred offspring have reduced survival or are of poorer quality. Embryos collected from spawning events in tanks of sister–brotherunrelated male trios were analysed using microsatellite DNA analysis to determine parentage. Single and multiple paternity was observed across batches. In two tanks, the brother had greater spawning success than the unrelated male, however, females generally favoured unrelated males as spawning partners (p < 0.001). Offspring mortality, deformities, size, and hatching success were monitored in artificially fertilized inbred and non‐inbred crosses of cod embryos and larvae. Data were collected from 14 replicates. The presence of deformities, larval survival, and size were not significantly different, with the exception of body depth (offspring from unrelated crosses were slightly larger, p = 0.01). Per cent hatch was slightly higher in offspring of unrelated crosses. Although inbreeding was revealed to occur in farmed cod, we did not see much of an effect on offspring quality. However, sample size was relatively small, and effects may not be obvious after one generation of inbreeding. More interesting findings may come from examining the broodstock, where families of cod have been maintained for many years.