Growth, viability and genetic characteristics of GH transgenic coho salmon strains

Transgenic coho salmon strains containing an all-salmon growth hormone (GH) gene construct (OnMTGH1) have been examined. The transgene utilized is comprised of the metallothionein-B promoter driving the expression of the type-I growth hormone gene from sockeye salmon. Transgene DNA is integrated into the salmon genome, but is transmitted at low frequency from founder transgenic animals consistent with late integration following microinjection resulting in mosaic animals, whereas subsequent generations transmit transgene DNA as a stable Mendelian trait. Different families established from separate founder animals yield lines with unique growth characteristics suggesting important site-of-integration effects on transgene expression. Growth enhancement of transgenic salmon is initiated early, with advanced hatch timing but occurring also throughout the life history, particularly during the early phase in fresh water. GH transgenic fish showed precocious smoltification and onset of sexual maturation, but approximately normal adult body size, indicating that compression of the normal coho salmon life history is occurring. The viability of diploid GH transgenic salmon ranges from reductions to greater than that of controls among strains, and triploid transgenic animals had normal viability relative to diploid transgenic salmon. Triploid transgenic salmon display a reduction in growth rate relative to transgenic diploids, but are still significantly growth enhanced compared with nontransgenic controls. The distinct phenotypic characteristics of GH transgenic families suggest that evaluation for aquaculture and for risk assessments requires examination of strains on a case-by-case basis. Furthermore, strong effects of size at maturity in culture conditions were observed for nontransgenic wild strain coho salmon which were not apparent in GH transgenic salmon, indicating that strong genotype by environment effects strongly influence phenotype and complicate risk assessments. (C) 2004 Elsevier B.V. All rights reserved.