Growth-enhanced coho salmon invading other salmon species populations: effects on early survival and growth

The first genetically modified (GM) fish intended for human consumption has recently stimulated significant scientific discussion and regulatory scrutiny regarding food safety and environmental risks. Currently, no experiments with transgenic fish have been performed in nature, yet such data are needed to facilitate predictions of ecological consequences should engineered fish escape to the natural environment. To address this limitation, we conducted experiments under natural conditions but within a contained environment to assess the impact of invasion of growth-enhanced GM coho salmon Oncorhynchus kisutch (Walbaum) on survival and growth of three naturally cohabitating fishes: Chinook salmon O.tshawytscha (Walbaum), steelhead trout O.mykiss (Walbaum) and conspecific wild-type coho salmon. We found that the impact of stream-reared GM coho salmon on invaded specimens was similar to the impact of non-GM coho salmon. However, GM fish significantly reduced survival and growth of the invaded populations if they were first allowed to grow larger under hatchery conditions before being released.Synthesis and applications. Our results show that the ecological impact of fish genetically modified (GM) for rapid growth on closely related fish species may not be high in stream environments, unless these fish are first reared under culture conditions where they are able to realize their genetic growth potential. As such, first generation escapes of GM fish into the natural environment should be a main concern in the short term, whereas later generations, which are more similar to naturally occurring genotypes, are expected to have significantly weaker effects but which could persist for longer periods. Our results show that the ecological impact of fish genetically modified (GM) for rapid growth on closely related fish species may not be high in stream environments, unless these fish are first reared under culture conditions where they are able to realize their genetic growth potential. As such, first generation escapes of GM fish into the natural environment should be a main concern in the short term, whereas later generations, which are more similar to naturally occurring genotypes, are expected to have significantly weaker effects but which could persist for longer periods.