DAVIS, K. B.; PETERSON, B.; HKD-SNARC/ARS/USDA, Stuttgart, AR; CGRU/ARS/USDA, Stoneville, MSLike: Insulin-Like Growth Factor and IGF Binding Proteins in Sunshine Bass

Growth of fish is regulated by components of the pituitary-liver-somatic tissue axis. The influence of growth hormone from the pituitary is,in part, to stimulate the liver to synthesize and release insulin-like growth factors (IGF-I and IGF-2). IGF-I is now thought to have the direct effects on somatic tissues that result in growth. Plasma IGF-I is bound in the plasma to IGF-I binding proteins (IGFBP) and the role of the IGFBPs as growth regulators has only recently been appreciated. Sunshine bass is a hybrid between white bass and striped bass and is widely used in aquaculture. Females grow to be larger than males, however the reason for the size difference is not known. Plasma IGF-I and IGFBPs were measured in sunshine bass of both sexes before and after a low-water confinement stress. IGF-I concentrations were 78.9 + 4.8 ng/ml in undisturbed fish and were not statistically different between males and females. Two hours after a 15 minute low water stress, concentrations were 82.2 + 4.7 ng/ml and were not statistically different between males and females. Plasma concentrations of a 33-kDa IGFBP were 96.6 + 16.6 arbitrary density units in undisturbed fish, were not significantly different between the sexes, and were not affected by low-water confinement. The growth difference between males and females in sunshine bass cannot be explained by concentrations of IGF-I or the 33-kDa IGFBP.