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Testing the Waters for Growth-Enhanced Salmon

But a study designed to address this subject using genetically engineered salmon suggested this wouldn't be a problem. When mixed with their wild-type cohorts, the modified salmon tried aggressively to compete, but failed.

The study found that at least in a laboratory setting, modified and wild-type salmon do not compete with each other unless there is a food shortage. 

A key factor in determining how disruptive an animal is to an ecosystem is its ability to compete for food. A transgenic animal of particular concern, called growth hormone (GH) salmon, is engineered to grow up to seven times larger than wild-type salmon. However, it is unknown whether GH salmon simply grow large whenever food is plentiful, or whether an enhanced appetite causes them to actively compete for food. 

To examine the competitive abilities of GH salmon, Robert Devlin and colleagues of Fisheries and Oceans Canada put engineered and wild-type salmon together, supplying either low or abundant levels of food. In the presence of sufficient food, the modified animals did not competitively interfere with the wild-type ones. 

When food was low, dominant fish, which were usually he engineered type, competed aggressively for food and sometimes cannibalized their cohorts. Ultimately, however, with little food the transgenic salmon populations crashed, often resulting in complete extinction. Meanwhile, nontransgenic salmon populations survived and multiply. These results show food availability and population structure strongly influence how transgenic salmon will impact an ecosystem, the researchers said.

The authors caution that effects observed in laboratory studies have uncertain applicability to complex natural ecosystems. The study is published in the June 7 early online edition of the Proceedings of the National Academy of Sciences, a research journal.