Interaction between ovine growth hormone and triiodo-L-thyronine on metabolic reserves of rainbow trout,Salmo gairdneri

Rainbow trout (Salmo gairneri) were given slow-release coconut oil implants which contained triiodo-L-thyronine (T3) and were subsequently administered ovine growth hormone (oGH) (either 0.24 or 2.5 g/g body weight) or saline every seventh day for four injections. The purpose of the study was to examine the interactions between oGH and T3 on several aspects of the metabolism in rainbow trout.Trout treated with T3 alone had higher carcass water content, lower liver glycogen, higher plasma T3 levels and lower plasma cholesterol, triglyceride and protein levels compared with the controls implanted with coconut oil implants alone. Trout treated with oGH alone had higher condition factors, lowered carcass total lipid content, elevated liver lipid and RNA content, and elevated plasma T3 and L-thyroxine (T4) levels compared with the coconut oil-implanted and saline-injected controls. Trout treated with T3 and oGH had lower liver glycogen content, higher plasma T3 and fatty acid levels and lower plasma T4, cholesterol and triglyceride levels compared with the controls given coconut oil implants and saline injections alone. There were no apparent effects of either hormone alone or in combination on liver: body mass ratios, liver DNA content, liver RNA:DNA ratios, liver RNA:protein ratios, liver protein:DNA ratios and liver protein content.The data suggest an interaction between oGH and T3 as regards the regulation of condition factor, carcass water content, carcass and liver total lipid content, liver RNA content, plasma fatty acid and plasma protein content.