ARS | Publication request: EFFECTS OF RECOMBINANT BOVINE GROWTH HORMONE (RBGH; POSILAC) ON GROWTH AND MRNA EXPRESSION OF IGF-I AND IGF-II IN CHANNEL CATFISH (ICTALURUS PUNCTATUS)

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 6, 2005
Publication Date: April 1, 2005
Citation: Peterson, B.C., Waldbieser, G.C., Bilodeau, A.L. 2005. Effects of recombinant bovine somatotropin on growth and abundance of mRNA for IGF-I and IGF-II in channel catfish (Ictalurus punctatus). Journal of Animal Science 83:816-824.

Interpretive Summary: In an attempt to better understand growth regulation, research examined growth rates, circulating levels of insulin like growth factor-I (IGF-I), and mRNA expression levels of IGF-I and IGF-II in channel catfish administered recombinant bovine growth hormone (rbGH). In the first study, rbGH treated fish had 48% greater final weight, 14% greater total length, and 52% better feed efficiency compared to controls. In the second study, Circulating levels of IGF-I were increased in rbGH-injected fish compared to controls by day 14. Liver IGF-I and IGF-II mRNA was increased 4.3 and 14.4-fold, respectively, by d 1 in rbGH-injected fish compared to controls. Expression of muscle IGF-I and IGF-II mRNA was not different throughout the study. This research demonstrates that rbGH improves growth performance of channel catfish. The changes in expression and protein levels of IGF-I support the role of IGF-I in growth regulation of channel catfish.

Technical Abstract: Research was conducted to examine growth rates, circulating levels of IGF-I, and mRNA expression levels of IGF-I and IGF-II in channel catfish administered recombinant bovine growth hormone (rbGH; Posilac). In the first study, juvenile catfish (5.5 +/- 0.5 g) were randomly assigned to one of three treatments: 1) Sham-injected control (Sham) (needle puncture/week); 2) rbGH (30 ug/g BW/week, Posilac); and 3) Non-handled control (Control). At the end of the six-week study, the fish were weighed, measured for length, and feed efficiency was determined. Compared to sham and control treatments, rbGH treated fish had 48% greater final weight, 14% greater total length, and 52% better feed efficiency (P < 0.001). In the second study, juvenile catfish (41.1 +/- 1.5 g) were randomly assigned to one of two treatments: 1) Sham and 2) rbGH. Eight fish per treatment were sampled on d 0, 1, 2, 7, 14, and 21 for blood, muscle, and liver samples. Relative expression of IGF-I and IGF-II mRNA was determined by real time PCR and plasma levels of IGF-I were measured using a validated fluoroimmunoassay. Circulating levels of IGF-I were increased (37.9 +/- 5.5 ng/ml vs 22.0 +/- 6.6 ng/ml; P < 0.05) in rbGH-injected fish compared to sham-injected controls by d 14. Liver IGF-I and IGF-II mRNA was increased 4.3 and 14.4-fold, respectively, by d 1 in rbGH-injected fish compared to controls (P < 0.05). However, expression of liver IGF-I and IGF-II mRNA was not different from controls on d 0, 2, 7, 14, and 21. Expression of muscle IGF-I and IGF-II mRNA was not different in rbGH-injected fish compared to controls throughout the study. Results of the first study demonstrated that rbGH improves growth performance of channel catfish. Results of the second study showed that the growth promoting effects of rbGH were not mediated by the expression of IGF-I or IGF-II mRNA 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 the role of IGF-I in growth regulation of channel catfish.