Cultured growth hormone transgenic salmon are reproductively out-competed by wild-reared salmon in semi-natural mating arenas

Abstract: The production of growth hormone (GH) transgenic animals has raised a host of social and scientific concerns regarding their potential impacts on ecosystems should they escape into nature. Indeed, theoretical models suggest that GH transgenic animals could, under specific conditions, decimate local populations. However, while there are numerous laboratory examinations of factors affecting survival of transgenic and wild animals, we know little about the competitive reproductive capacity of transgenic animals. Here, we examined the reproductive capabilities of cultured GH transgenic coho salmon (Oncorhynchus kisutch) when in competition with wild coho derived from nature using semi-natural mating arenas (within a contained facility). To account for the well-known reproductive impairments associated with culturing salmon in laboratory facilities we contrasted the competitive reproductive success of GH transgenic coho against that of cultured non-transgenic coho. We also performed in vitro sperm analyses to assess the postcopulatory competitive ability of GH transgenic coho. In competitive mating arenas, transgenic coho performed fewer courtship and aggressive behaviours than coho from nature and sired less than 6% of offspring. Non-transgenic cultured coho, despite their smaller body size, sired more than twice as many offspring than transgenic coho when competing against wild coho in mating arenas. Transgenic males also face a postcopulatory reproductive disadvantage as their ejaculates contained fewer sperm that swam slower and for shorter durations than sperm from wild males. Together, these findings suggest limited potential for the transmission of transgenes from cultured GH transgenic coho salmon through natural matings should they escape from a contained culture facility into nature and reproductively interact with a local wild coho salmon strain. However, as responses of wild-reared fish can differ greatly from those of cultured fish, we stress the importance of understanding genotype-by-environment interactions for reproductive phenotypes when developing risk assessment information. [Copyright &y& Elsevier]