Influence of reproductive status, sex hormones and temperature on plasma IGF-I concentrations in sunshine bass (Morone chrysops × Morone saxatilis)

Insulin-like growth factor-I (IGF-I) concentrations in male and female sunshine bass (Morone chrysops × 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 tended to be higher in male fish and increased as pond temperature and feeding increased in both sexes. Gonadal development was greatest 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. 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 temperature in the ponds, and were inversely related to gonadal development and sex hormones. Exogenous sex hormones resulted in a decrease in plasma IGF-I, feeding activity and growth.