Using purposeful inbreeding to reduce outbreeding depression caused by escaped farmed Atlantic cod

Abstract

Fish often escape from aquaculture operations, raising concerns of interactions with wild individuals. Farmed fish from genetically diverse populations grown outside their native range create the threat of outbreeding depression if they escape and interbreed with wild fish. Atlantic cod Gadus morhua spawn within cages, releasing millions of embryos into the environment, some of which may live to reproduce. Due to selective breeding, fewer breeding individuals are used in culture relative to wild populations, potentially leading to inbreeding within single cages. If inbreeding reduces survival, this could reduce the likelihood of outbreeding depression if maturing escaped cod mate with wild cod. Forced inbreeding could be used to mitigate some effects of aquaculture on the environment. We aimed to determine if cod inbreed and, if so, what short-term effects inbreeding has on offspring. Spawned embryos from tanks of sister-brother-unrelated male trios underwent microsatellite analysis to determine parentage. Inbreeding occurred, and females did not prefer one type of male over the other. Percent hatch, deformities, larval size, and mortality were monitored in artificially fertilized inbred and unrelated crosses. Percent hatch was higher in non-inbred offspring, but inbreeding had no significant effect on the other factors.