Growth of growth hormone transgenic coho salmon Oncorhynchus kisutch is influenced by construct promoter type and family line

Several different transgenic growth hormone (GH) gene constructs have been used to obtain accelerated growth in salmonids. However, there have been limited direct comparisons of these constructs in terms of the ability to achieve maximal growth in fish. We examined the effect of promoter type (sockeye salmon metallothionein-B or histone 3) fused to a growth hormone-1 coding region from the same species (OnMTGH1 and OnH3GH1 constructs respectively) on growth and plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) in multiple strains of GH transgenic coho salmon (Oncorhynchus kisutch). Salmon transgenic for the OnMTGH1 construct had consistently greater overall weight than those containing the OnH3GH1 construct, although both groups possessed greatly accelerated growth over non-transgenic fish. However, there were strong strain effects, where some OnH3GH1 strains had similar weight to OnMTGH1 strains while others did not. Triploidy diminished growth acceleration and decreased condition factors in both a fast growing MT strain and slower growing H3 strain. Plasma GH levels did not correlate to weight in transgenic strains, and all but one transgenic strain had plasma GH levels similar to equal sized non-transgenic fish. In contrast, plasma IGF-I content correlated well to size in transgenic strains. The mechanism by which accelerated growth in transgenic fish is obtained appears to be due in part to an upregulation of GH action through increased circulating IGF-I levels, and promoter-type appears to influence potential for growth.

► Growth hormone (GH) transgenesis causes accelerated growth in fish.
► Use of different constructs to increase growth has not been directly compared.
► Metallothionein was a better promoter than histone at promoting growth.
► Growth was greatly affected by strain and triploidy, as well as construct type.
► Growth correlated to plasma IGF-I levels, but not GH levels, in transgenic strains.