A Potent Analog of Recombinant Bovine Somatotropin Accelerates Growth in Juvenile Coho Salmon (Oncorhynchus kisutch)

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Abstract
Recombinant bovine somatotropin and a recently engineered analog of bovine somatotropin were compared for their growth-promoting ability in underyearling coho salmon (Oncorhynchus kisutch). Treated fish were given five biweekly intraperitoneal injections of one of the hormone preparations at either 0.2 or 2.0 μg/g body weight. Both substances significantly enhanced growth, and by the end of the treatment period the fish injected with the high dose of the analog were significantly larger than all other groups, being 43.5% heavier than the sham-treated (saline injected) fish. Fish treated with the high dose of the native form of somatotropin were 25.3% heavier than the sham-treated group, but were not significantly different in size from fish treated with the low dose of analog. A four-point bioassay indicated that the analog had approximately nine times the growth-promoting potency of the native form of bovine somatotropin in coho salmon. Food conversion efficiency was improved by somatotropin therapy, but all groups exhibited a similar osmoregulatory capacity when subjected to a 24-h seawater challenge during the posttreatment period. Given the economic feasibility of producing recombinant proteins in large quantities, this analog has the potential to improve the production characteristics of cultured salmon.