SEASONAL CYCLES IN THE SONIC MUSCLES OF THE WEAKFISH, CYNOSCION REGALIS

Male weakfish, Cynoscion regalis, were collected from the southwest po rtion of Delaware Bay from April through September in 1990 and 1991. M orphometric measurements of the sonic muscles, testis size (gonadosoma tic index, or GSI), and plasma androgen concentrations were recorded t o obtain data on the seasonality of sonic muscle condition and its rel ationship with the timing of reproduction in this population. The soni c muscles were bilaterally symmetrical and showed no significant seaso nal differences in length or width across both collecting periods. Son ic muscle thickness did change significantly across both collecting pe riods and there was a threefold increase in sonic muscle mass during t he course of each collecting period. GSI and levels of both plasma tes tosterone and 11-ketotestosterone also varied significantly across bot h collecting seasons. Changes in sonic muscle mass followed but lagged one to three weeks behind the rise and fall in plasma androgen levels . Pertinent models of skeletal muscle hypertrophy and atrophy are disc ussed as is the possibility that increased sonic muscle mass during th e spawning season may increase the reproductive fitness of male weakfi sh.