Stimulation of coho salmon growth by insulin-like growth factor I

The effect of insulin-like growth factor I on growth rate of coho salmon (Oncorhynchus kisutch) was examined. Juvenile coho salmon received implants of osmotic minipumps containing recombinant bovine insulin-like growth factor I (rbIGF-I) or saline for a period of 3 to 4 weeks. High doses of rbIGF-I (greater than 0.13 microgram.g-1.d-1) resulted in hypoglycemia and death. In 2-year-old coho salmon, 0.09 microgram.g-1.d-1 rbIGF-I administered for 25 days doubled linear growth rate and increased growth rate in weight by 40%. In rapidly growing, 1-year-old coho salmon, growth rate was not altered by rbIGF-I at 0.01 or 0.05 micrograms.g-1.d-1 for 31 days. In ration-limited fish exhibiting slow growth in the control group, rbIGF-I (0.02 microgram.g-1.d-1) increased linear growth rate by up to threefold and growth rate in weight by up to fourfold. The results indicate that exogenous treatment with mammalian IGF-I can stimulate coho salmon growth under some conditions, and that endogenous IGF-I may be an important factor in regulating growth of teleosts.