Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2010
Publication Date: 1/5/2011
Citation: Davis Jr, K.B., Mcentire, M.E. 2011. Influence of reproductive status, sex hormones and temperature on plasma IGF-I concentrations in sunshine bass (Morone Chrysops X Morone Saxatilis). Comparative Biochemistry and Physiology. 158A:13-16. Interpretive Summary: Plasma IGF-I concentrations of market sized sunshine bass were studied in commercial ponds from March through April when water temperatures were increasing and spawning occurred. Gonadal development, plasma estradiol and testosterone IGF-I concentrations fell during the study and plasma IGF-I concentrations increased. When estrogen and methyl testosterone were fed to immature fish in indoor tanks, feeding both hormones reduced feeding activity and growth. Further, plasma IGF-I concentrations were lower in hormone fed fish than in controls. Methyl testosterone is not androgenic in sunshine bass and plasma estrogen concentrations do not appear to be responsible for the gender bias in weight for female sunshine bass.
Technical Abstract: Insulin-like growth factor-I (IGF-I) concentrations in male and female sunshine bass (Morone chrysops X Morone saxatilis) were determined in March, early April, and late April in outdoor ponds at a commercial farm. Female fish were always larger than male fish, however plasma IGF-I concentrations were tended to be higher in male fish and increased as pond temperature increased in both sexes. Gonadal development was largest in both sexes in March and declined to a regressed state by the end of April and the same pattern of change occurred with plasma estrogen and testosterone. Growth and IGF-I concentrations in sunshine bass fed estrogen, methyl testosterone, or a control diet were also determined. Growth was reduced in fish fed both sex hormones, although the effect of estrogen was the most pronounced. Fish fed the control diet had the highest IGF-I levels, androgen fed fish had intermediate levels, and estrogen fed fish had the lowest IGF-I concentrations after 4 weeks on the diet. Plasma IGF-I concentrations appeared to respond to increasing temperatures in the ponds and were inversely related to sex hormones. Exogenous sex hormones resulted in a decrease in plasma IGF-I, feeding activity and growth. Plasma IGF-I or plasma estrogen concentrations do not appear to explain the sexually dimorphic growth in sunshine bass.