Seawater adaptability and hormone levels in growth-enhanced transgenic coho salmon, Oncorhynchus kisutch

Abstract

Transgenic coho salmon containing a growth hormone (GH) gene construct have been examined for their hormone levels and ability to osmoregulate in sea water. Relative to their smaller nontransgenic siblings (age controls), GH-transgenic coho precociously develop external phenotypes and hypo-osmoregulatory ability typical of smolts. Specific growth rates of the transgenic coho were approximately 2.7-fold higher than older nontransgenic animals of similar size, and 1.7-fold higher than their nontransgenic siblings. GH levels were increased dramatically (19.3- to 32.1-fold) relative to size control salmon, but IGF-I levels were only modestly affected, being slightly enhanced in one experiment and slightly reduced in another. Insulin levels in transgenic animals did not differ from size controls, but were higher than nontransgenic siblings, and thyroxine levels in transgenic animals were intermediate between levels found in size and age controls. The homeostatic controls of, and interactions among, these hormones are discussed with respect to their effects on growth and osmoregulation.