700 



Fishery Bulletin 92(4). 1994 



3.3 and 3.5% of TW by the peak of the spawning sea- 

 son in both years and decreased to roughly 1% of TW 

 by the fall (Fig. 2). These seasonal changes in SMSI 

 represent a threefold increase in sonic muscle mass. 



Sonic muscle color also changed seasonally, follow- 

 ing the changes in sonic muscle thickness. The sonic 

 muscles were a dark blood-red throughout May and 

 most of June. During late June and July muscle color 

 faded to a dark pink, and in August to a light pink. 

 During September and October sonic muscle color 

 faded to a dark yellow and the muscle tissue became 

 semitranslucent. 



There were no significant seasonal changes in the 

 mean sonic muscle length in either 1990 or 1991. 

 SMLI values remained between 6 and 7% of TL across 

 the entire collecting period during both years. A sig- 

 nificant seasonal change in mean sonic muscle width 

 was noted in 1990 but not in 1991. SMWI ranged 

 from 28.6 to 30.8% of TL in 1990 and from only 28.3 

 to 29.2% of TL in 1991. 



Total testis weight changed significantly across the 

 collecting period in both 1990 and 1991. GSI values 

 rose to a maximum of 4.2%> of TW in both collecting 

 seasons. After the peak of the spawning season, GSI 

 values decreased rapidly, reaching postspawning 

 lows between 0. 1 and 0.2% of TW in the early fall 

 (Fig. 3A). 



Plasma androgen levels also varied significantly 

 during both collecting seasons. Total plasma test- 

 osterone titers were somewhat lower in 1990, reach- 

 ing a maximum of only 3.34 ng-mL -1 , whereas 1991 

 values climbed to 5.5 ngmL 1 (Fig. 3B). In both years 

 levels decreased to postspawning values of between 

 1.2 and 1.6 ng-mL 1 . Unbound plasma 11-keto- 

 testosterone levels followed a trend similar to that 

 noted for total plasma testosterone during both col- 

 lecting periods (Fig. 3C). Maximal levels of unbound 

 11-ketotestosterone reached 1.1 ng-mL -1 in both years 

 and then decreased to less than 0.1 ng-mL" 1 

 by the fall. 



Examination of weakfish in 1991 indicated that 

 virtually all the specimens were capable of drum- 

 ming when handled throughout the entire collecting 

 period, regardless of changes in sonic muscle condi- 

 tion. Specimens produced milt throughout most of 

 the study period, although no milt could be obtained 

 before mid-May and none was obtained after mid- 

 August. 



Discussion 



The extreme seasonality of drumming activity in 

 sciaenids (Fish and Cummings, 1972; Takemura et 

 al., 1978; Mok and Gilmore, 1983; Saucier and Baltz, 



a 



E 



DO 



Apr 26 May 26 



Jun 25 Jul 25 

 Date 



Aug 24 Sep 23 



Figure 3 



(A) Gonadosomatic index (GSI); (B) plasma testoster- 

 one concentration; (C) and unbound plasma 11-keto- 

 testosterone concentration of the weakfish, Cyno- 

 scion regalis, plotted across sampling date for the 

 1990 and 1991 collecting seasons. Points are means 

 (n=3-10 fish) ± one standard error of the mean. 



1993 ) suggests that the condition of the sonic muscles 

 in these species may not remain constant through- 

 out the year. The data presented here indicate that 

 the condition of the sonic muscles of weakfish does 

 change seasonally; there was an approximate three- 

 fold difference in mass between the spawning and 

 pre- or post-spawning periods. As the sonic muscle 

 could not grow beyond its points of attachment 

 (Tower, 1908; Ono and Poss, 1982), which define the 

 length and width of the muscle, seasonal hypertro- 

 phy was expressed as an increase in muscle thick- 

 ness. Seasonal changes in sonic muscle condition 

 have not been documented in other sciaenids; how- 



