Sustained predation effects of hatchery‐reared transgenic coho salmon Oncorhynchus kisutch in semi‐natural environments

Abstract

Summary 1. The potential risks of accidental or intentional introduction of transgenic organisms to nature are unknown. We have previously shown that, after being reared in the hatchery, growth hormone transgenic coho salmon Oncorhynchus kisutch can exert a stronger predation effect on natural prey under simulated natural conditions compared with hatchery‐reared genetically wild conspecifics. However, when reared in a simulated natural environment, the difference between the two genotypes was greatly reduced. 2. Here, we tested if the difference in predation rate between the two genotypes after being reared in the hatchery diminishes with time spent in a simulated natural environment. Genetically wild coho salmon reared in the hatchery were size matched to younger satiation‐fed (fast‐growing) and same age restricted‐fed (growth rates matched to wild‐type) transgenic fish. These three types of predators were released into simulated natural habitats and their effects on prey survival and growth were monitored over a 2‐month period. 3. Restricted‐fed, but not satiation‐fed, transgenic predators consumed significantly more prey (×2·7) relative to wild predators during the first month, with an increase to 3.8 times during the second period. Prey biomass decreased more in the presence of restricted‐fed predators during the first period, but a faster growth of these prey during the second period compensated for the higher predation rate resulting in no significant difference in prey biomass among predators after 2 months. Transgenic predators grew more in length than wild type, but all three types converged in weight and condition over time. 4. Synthesis and applications. Behavioural phenotypes developed in the hatchery showed little plasticity after release. Hence, development of policy on the use of transgenic organisms must incorporate knowledge of the effect of environmental conditions, experienced by the organism prior to escape or release, on phenotype. The risk posed by culture‐reared organisms may depend on the frequency of escapes, number of individuals escaping and age of escapees. Important to note is that wild‐reared organisms may be biologically different from culture‐reared and thus require separate evaluation. Our results will be important for science policy makers and regulators to consider when deciding whether to allow commercial application of transgenic species in aquaculture.