Watered-down fish

Natural History, Feb, 2004 by Stephan Reebs

Aquaculture has brought down the price of salmon considerably, but it's also raised concerns. An estimated 2 million farm-raised salmon escape each year in the North Atlantic alone. The worry has been that farm fish strains may have lost certain genes that enhance survival in the wild; if the farm fish mate with wild fish their progeny may turn out to be poor survivors in the wild, ultimately undermining the genetic fitness of the wild population.

Recent experimental evidence suggests such fears are justified. Philip McGinnity, an ichthyologist at the Marine Institute in Newport, Ireland, and his coworkers recorded the ancestry and then tracked the success of wild, farm, and wild-farm hybrid Atlantic salmon at multiple stages of their life history.

At every stage, the wild fish were the fittest. Wild juveniles were the most likely young to survive, and wild adults were the most likely adults to return and breed. Having even one farm salmon as a parent or grandparent hobbled a fish's chances; having two farm ancestors reduced the chances even further. The pure farm salmon fared the worst: very few returned to lay eggs. ("Fitness reduction and potential extinction of wild populations of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon," Proceedings of the Royal Society of London B 270:2443-50, December 7, 2003)