PETERSON, B.C.; WALDBIESER, G.C.; BILODEAU, L.; USDA/ARS; USDA/ARS; USDA/ARS: Effects of recombinant bovine growth hormone (rbGH; Posilac) on growth and mRNA expression of IGF-I and IGF-II in channel catfish.

Growth is a valued trait for cultivated fish. Identifying genes involved in regulating growth may prove important to selecting fish for efficient lean growth. Expression of IGF-I and IGF-II in relation to accelerated growth in channel catfish has not been previously examined. Research was conducted to examine growth rates, IGF-I, and IGF-II mRNA expression in catfish administered recombinant bovine growth hormone (rbGH; Posilac). Ninety fish (5.5 � 0.5 g) were randomly assigned to one of three treatments with three replicates each. The treatments were: 1) Sham injected control (needle puncture/week); 2) rbGH (30 mg/g BW/week, Posilac); and 3) Non-handled control. At the end of the six-week study, the fish were weighed, measured for length, and muscle and liver samples were excised. Final weight was increased (P < 0.01) 48% in the rbGH-treated fish compared to the average final weights of the sham and non-handled controls (25.5 � 0.5 g vs 17.2 � 0.6 g). rbGH treatment also increased total length (14.3 � 0.2 cm vs 12.5 � 0.4 cm; P < 0.01). Current data indicates that expression of IGF-I was higher than IGF-II in muscle and liver in all treatments. There was no difference in expression of IGF-I or IGF-II mRNA in muscle or liver of rbGH-injected fish compared to controls. Results of this study demonstrate that rbGH can increase growth rates in catfish, and suggest rbGH may be acting directly on target tissues to mediate the observed growth response. Future examination of circulating levels of IGF-I and IGF-II, as well as GH receptor mRNA expression, may also contribute to our understanding of muscle growth in channel catfish.