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

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-osmoregul atory ability typical of smolts. Specific growth rates of the transgenic co ho were approximately 2.7-fold higher than older nontransgenic animals of s imilar size, and 1.7-fold higher than their nontransgenic siblings. GH leve ls were increased dramatically (19.3- to 32.1-fold) relative to size contro l salmon, but IGF-I levels were only modestly affected, being slightly enha nced in one experiment and slightly reduced in another. Insulin levels in t ransgenic animals did not differ from size controls, but were higher than n ontransgenic siblings, and thyroxine levels in transgenic animals were inte rmediate between levels found in size and age controls. The homeostatic con trols of, and interactions among, these hormones are discussed with respect to their effects on growth and osmoregulation. (C) 2000 Elsevier Science B .V. All rights reserved.