Comparison of growth rates between growth hormone transgenic and selectively-bred domesticated strains of coho salmon (Oncorhynchus kisutch) assessed under different culture conditions

Aquaculture continues to be the fastest-growing animal food sector and accounts for over 50% of the world's fish consumption. This trend is projected to continue, highlighting the role that the aquaculture industry will play in ensuring future global food security. Enhancement of growth rates of fish can optimize aquaculture production and has been achieved through selective breeding programs producing fast-growing domesticated strains, or the development of growth hormone (GH) transgenic strains. Although the ability of selectively-bred domesticated and GH transgenic salmon to outgrow wild-type salmon is well documented, very little research has been reported that directly compares the growth rates of domesticated and GH transgenic strains. The aim of the present study was to compare the growth and survival of selectively-bred domesticated and GH transgenic coho salmon across a range of experimental conditions. We performed four experiments investigating the growth rates of domesticated and GH transgenic salmon by comparing these strains at different developmental stages and under different experimental rearing conditions, as well as under conditions when strains were competing and when they were reared separately. Results from all experiments showed that GH transgenic coho salmon grew faster and to a larger size than the selectively-bred domesticated coho salmon. This was true whether fish groups were reared post-smolt in freshwater or seawater, whether reared together or separately, and whether manipulated to be size-matched at early stages. Thus, GH transgenesis could become a viable complement to selective breeding to produce fast-growing salmon for aquaculture systems. While further research can continue to optimize the development and use of transgenic strains, the data presented here also are important for environmental risk assessments by providing data on the relative fitness and ecological consequences of selectively-bred domesticated and GH transgenic fish should they enter nature.