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Posted: December 2014

Genetically Modified Atlantic Salmon/Brown Trout Hybrids Have Unexpected Ecological Effects

Researchers in Canada bred hybrids between genetically modified (GM) Atlantic salmon and their close relative, the brown trout. The GM salmon eggs and sperm used in the experiment were obtained from the company AquaBounty, which has applied for commercial release of this GM salmon. The modified salmon grows to maturity much more rapidly than does wild salmon; it contains a growth hormone gene from the Pacific Chinook salmon and a promoter from ocean pout. Because brown trout and Atlantic salmon are known to mate and form viable hybrids — albeit seldomly — in the wild, the researchers wanted to explore what physiological and ecological features GM salmon/brown trout hybrids might have.

They successfully bred GM salmon/brown trout hybrids. The growth hormone gene construct was passed on to 43 percent of the hybrids. The others did not carry the transgene. The hybrids were grown in hatcheries and subsequently in a “stream mesocosm” that mimicked some natural conditions (live food, restricted food supply, unidirectional water flow, and so on). Here are some of the results:
  • Like their transgenic parent, the transgenic hybrids grew significantly larger than wild Atlantic salmon or wild brown trout during the 100 days in the hatchery environment.
  • In the hatchery environment the transgenic hybrids had a faster growth rate than even the GM Atlantic salmon.
  • Surprisingly, when the transgenic hybrids were grown together with GM salmon or wild salmon in the stream mesocosms (in which food supply was limited), the transgenic hybrids suppressed the growth rate of the other fish in this juvenile phase of growth:
    • The growth rate of wild-type salmon was reduced by 54 percent compared to when they developed without the hybrids in their environment.
    • The growth rate of GM salmon was reduced by 82 percent compared to when they developed without the hybrids in their environment.
  • In the stream mesocosms, the transgenic hybrids grew over 80 percent faster than the GM salmon.
These results show that in the semi-natural mesocosms the transgenic hybrids — for unknown reasons — have an advantage over both the parental GM salmon and wild salmon. As the researchers remark, if hybrids were to arise in the wild and such an advantage were maintained, then “transgenic hybrids could detrimentally affect wild salmon populations.” Or stated differently: “complex competitive interactions associated with transgenesis and hybridization could have substantial ecological consequences for wild Atlantic salmon.”

Proponents of the commercial approval of GM salmon — which is still being considered by the U.S. Food and Drug Administration as of fall 2014 — argue that should GM salmon accidentally be released into the environment, they would pose no threat to wild salmon because under the limited food supply conditions in nature they would not thrive. But the research by Oke et al. presents the surprising finding that GM salmon/brown trout hybrids may be remarkably vital. The authors conclude: “Ultimately, we suggest that hybridization of transgenic fishes with closely related species represents potential ecological risks for wild populations and a possible route for introgression of a transgene, however low the likelihood, into a new species in nature.”

Oke, K. B., P. A. H. Westely, D. T. R. Moreau et al. (2014). “Hybridization Between Genetically Modified Atlantic Salmon and Wild Brown Trout Reveals Novel Ecological Interactions,” Proceedings of the Royal Society B 280:20131047.

Copyright 2014 The Nature Institute.

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