EFFECTS OF EXOGENOUS TESTOSTERONE ON SONIC MUSCLE MASS IN THE WEAKFISH, CYNOSCION REGALIS

Three testosterone (T) implant experiments were carried out to investi gate the hormonal control of seasonal hypertrophy in the sound produci ng, or sonic, muscles of the weakfish Cynoscion regalis. The first exp eriment examined the role of T in the seasonal increase in sonic muscl e mass noted in adult male weakfish during the spring and summer spawn ing period. Specimens held over-winter were implanted with T or vehicl e prior to the natural spawning season. The sonic muscle mass of the T -implanted group increased two and a half-fold over a period of 3 week s, while that of the sham-implanted group did not change. At the end o f the experiment. the cross-sectional area of the sonic muscle fibers in the T-implanted group averaged 500 mu m(2), while that of the sham- implanted group averaged 300 mu m(2). In a second experiment, the elev ated sonic muscle mass of spawning male weakfish was sustained with ph armacological levels of plasma T for a period of 4 months following th e spawning season. The sonic muscle mass of the sham-implanted group d ecreased to typical postseason values. In a third experiment. male and female age-0 weakfish were held over-winter and then implanted with T in advance of their first natural spawning season. The sonic muscles of the T-treated male specimens attained twice the mass of those of th e sham-implanted male specimens in 3 weeks time. No sonic muscle devel opment was noted in any of the female specimens. (C) 1995 Academic Pre ss, Inc.