The evolutionary fitness of Atlantic salmon is being damaged by genetic contamination as wild fish breed with escapees from fish farms. When wild Atlantic salmon breed with escaped farmed salmon, their descendants grow faster and mature at a younger age, undermining the ability of the species to survive and reproduce in its natural environment.
Aquaculture is expected to meet most of the world’s extra demand for fish in the coming decades. Fish farming can harm wild populations in various ways, from genetic contamination to disease, but most of our understanding of these dangers has been gleaned from experiments in laboratories and controlled settings.
To get a better idea of how the spread of farmed salmon’s genes is affecting wild fish, Geir Bolstad at the Norwegian Institute for Nature Research in Trondheim and his colleagues collected scales from 7000 adult salmon in 105 rivers in Norway, the world’s biggest producer of farmed fish. By examining a scale from each fish and genotyping just over half of them, the team analysed what genetic ancestry with farmed fish means for their pace of development.