Submitted to: Domestic Animal Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/14/2005
Publication Date: 1/6/2006
Citation: Small, B.C., Murdock, C.A., Waldbieser, G.C., Peterson, B.C. 2006. Reduction in channel catfish hepatic growth hormone receptor expression in response to food deprivation and exogenous cortisol. Domestic Animal Endocrinology 31:340-356. Interpretive Summary: Farmed channel catfish are sometimes subjected to periods of restricted feeding as a means of managing poor water quality and disease outbreaks. Stressful situations such as these can also lead to an increase in blood concentrations of the stress hormone cortisol. Both restricted feeding and stress result in reduced fish growth and have a negative economic impact to the farmer. In the present study we sought to identify a gene in catfish that is known to control growth in other animals, and to assess how that gene is controlled during restricted feeding and periods of elevated blood cortisol concentrations. The gene, growth hormone receptor, was successfully isolated from channel catfish and was found to be negatively regulated by both restricted feeding and elevated blood cortisol. These results provide new information about the control of catfish growth and will aid in the development of management techniques for improving fish growth. Catfish growth hormone receptor is also being looked at as a possible marker for selecting faster growing catfish as part of a selective breeding program.
Technical Abstract: The objective of this study was to assess the effects of food deprivation and exogenous cortisol administration on somatic growth of channel catfish, Ictalurus punctatus, and examine the resultant changes in circulating insulin-like growth factor-I (IGF-I) concentrations and growth hormone receptor (GHR) gene expression. Integral to this objective, we report the isolation, sequence, and characterization of channel catfish GHR. Sequence analysis and characterization results indicate sequence identity and tissue distribution similar to GHRs in other teleost fish and several functional characteristics conserved in known vertebrate GHRs. The effects of food deprivation and dietary exogenous cortisol administration were assessed as part of a 4-wk study. Growth was significantly reduced after 4 wk in cortisol-fed fish compared to fed-control fish, and fasting resulted in weight loss. At the end of the 4-wk study, both IGF-I plasma concentrations and hepatic GHR mRNA abundance were significantly reduced in fasted and cortisol-fed catfish. Levels of hepatic GHR mRNA were positively correlated to circulating IGF-I levels. These results suggest that a reduction in hepatic GHR gene expression might serve as a mechanism for the reduction of circulating IGF-I and growth in channel catfish during periods of food deprivation and stress.