Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2004
Publication Date: July 25, 2004
Citation: Peterson, B.C., Waldbieser, G.C. 2004. Muscle and liver IGF-I mRNA expression and plasma IGF-I levels in channel catfish administered rbGH over time. Abstract, 2004 ADSA-ASAS-PSA Joint Annual Meeting. St. Louis, MO, July 25-29, 2004, p. 194. Technical Abstract: We have previously reported increased growth rates of 48% in as little as six weeks in channel catfish administered recombinant bovine growth hormone (rbGH). Identifying genes involved in regulating growth may prove important to selecting fish for efficient lean growth. Research was conducted to examine plasma IGF-I and IGF-I mRNA expression in the muscle and liver of catfish administered rbGH. Ninety-six fish (41.1 +/- 1.5 g) were randomly assigned to one of two treatments with four replicates each. The treatments were: 1) Sham-injected control (needle puncture/week) and 2) rbGH (30 micrograms/g BW/week, Posilac). Eight fish per treatment (2 fish/tank) were sampled on d 0, 1, 2, 7, 14, and 21. The fish were bled and muscle and liver samples were excised on each of the 6 sampling days. Relative expression of IGF-I mRNA was determined by real time RT-PCR. Circulating levels of IGF-I increased (55.5 +/- 2.5 ng/ml vs 22.2 +/- 1.7 ng/ml; P = 0.03) in rbGH-injected fish compared to sham-injected controls only at d 14. Expression of muscle IGF-I mRNA was not different in rbGH-injected fish compared to controls throughout the 21-day study. Liver IGF-I mRNA was increased 6-fold by d 1 in rbGH-injected fish compared to controls (P = 0.05). However, expression of liver IGF-I mRNA was not different from controls on d 2, 7, 14, and 21. Results of this study show that the growth promoting effects of rbGH were not mediated by the expression of IGF-I in the muscle. Instead, the results suggest that rbGH promotes growth by stimulating plasma IGF-I release, probably through its direct effect on the liver to synthesize IGF-I. The changes in expression and protein levels of IGF-I support IGF-I's role in growth regulation of channel catfish.