Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: August 4, 2004
Publication Date: January 17, 2005
Citation: Peterson, B.C., Small, B.C. 2005. The use of recombinant bovine growth hormone (rbGH; Posilac) to characterize the GH-IGF axis in channel catfish. Aquaculture America Conference. New Orleans, LA, Jan. 17-20, 2005, p. 323. Technical Abstract: As in mammals, the growth hormone-insulin like growth factor (GH-IGF) system plays an important role in the endocrine control of fish growth. However, the roles of the GH-IGF system in mediating growth in channel catfish, which represent a major aquaculture species in the southeastern United States, are not known. The present study was conducted to characterize the roles of GH, IGF-I, and IGF-II in channel catfish administered recombinant bovine growth hormone (rbGH). We have previously reported increased growth rates of 48% in as little as six weeks in channel catfish administered rbGH. In the present study, 96 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 body weight/week, Posilac). Eight fish per treatment (2 fish/tank) were sampled on d 0, 1, 2, 7, 14, and 21. The fish were euthanized and bled and muscle, liver, and pituitaries were excised on each of the 6 sampling days. A time-resolved fluoroimmunoassay was used to measure circulating plasma levels of IGF-I while relative expression of IGF-I, IGF-II, and GH mRNA was determined by real time 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 by d 14. Liver IGF-I and IGF-II mRNA increased 6- and 14.4-fold, respectively, by d 1 in rbGH-injected fish compared to sham-injected controls (P < 0.05). Expression of muscle IGF-I mRNA was not different between treatments throughout the study. However, muscle IGF-II mRNA was increased 7.9-fold by d 1 in rbGH-injected fish compared to sham-injected controls (P < 0.001). Pituitary GH mRNA expression was not different between treatments throughout the study. The results of this study demonstrate that high levels of exogenous rbGH do not cause a decrease in GH mRNA expression through a negative feedback loop in the pituitary. The results also 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. These data also provide evidence for a role of IGF-II in growth of channel catfish.