Abstract. — Male weakfish, Cy- 

 noscion regalis, were collected from 

 the southwest portion of Delaware 

 Bay from April through September 

 in 1990 and 1991. Morphometric 

 measurements of the sonic muscles, 

 testis size (gonadosomatic index, or 

 GSI), and plasma androgen concen- 

 trations were recorded to obtain 

 data on the seasonality of sonic 

 muscle condition and its relation- 

 ship with the timing of reproduc- 

 tion in this population. The sonic 

 muscles were bilaterally symmetri- 

 cal and showed no significant sea- 

 sonal differences in length or width 

 across both collecting periods. Sonic 

 muscle thickness did change sig- 

 nificantly across both collecting 

 periods and there was a threefold 

 increase in sonic muscle mass dur- 

 ing the course of each collecting 

 period. GSI and levels of both 

 plasma testosterone and 11- 

 ketotestosterone also varied sig- 

 nificantly across both collecting 

 seasons. Changes in sonic muscle 

 mass followed but lagged one to 

 three weeks behind the rise and fall 

 in plasma androgen levels. Perti- 

 nent models of skeletal muscle hy- 

 pertrophy and atrophy are dis- 

 cussed as is the possibility that in- 

 creased sonic muscle mass during 

 the spawning season may increase 

 the reproductive fitness of male 

 weakfish. 



Seasonal cycles in the sonic muscles 

 of the weakfish, Cynoscion regalis 



Martin A. Connaughton 



College of Marine Studies, University of Delaware 



700 Pilottown Road. Lewes. Delaware 19958 

 Present address UT-Houston Medical School, Laboratory for 

 Neuroendocrmology, PO. Box 20708, Houston, Texas 77225 



Malcolm H. Taylor 



School of Life and Health Sciences and College of Marine Studies 

 University of Delaware, Newark, Delaware 19716 



Manuscript accepted 21 April 1994. 

 Fishery Bulletin 92:697-703 ( 1994). 



Sound production is used by a num- 

 ber of teleost species during aggres- 

 sive or defensive behaviors ( Gray and 

 Winn, 1961; Steinberg et al., 1965; 

 Hawkins and Chapman, 1966; Horch 

 and Salmon, 1973; Hawkins and 

 Rasmussen, 1978), but the greatest 

 volumes of sound produced by teleo- 

 sts are associated with reproduction. 

 A number of marine families includ- 

 ing Batrachoididae (Gray and Winn, 

 1961; Fish, 1964), Blenniidae 

 (Tavolga, 1958b), Gadidae (Hawkins 

 and Rasmussen, 1978), Gobiidae 

 (Tavolga, 1958a), Triglidae (Moulton, 

 1956), Sciaenidae (Hildebrand and 

 Schroeder, 1928; Pearson, 1929; 

 Burkenroad, 1931), Serranidae, and 

 Scaridae (Lobel, 1992) produce sound 

 during the spawning season. Cho- 

 ruses of these sounds are generally 

 limited to the season and geographic 

 area in which the species in question 

 spawns (Fish and Cummings, 1972; 

 Fine, 1978; Takemura et al., 1978; 

 Mok and Gilmore, 1983; Saucier and 

 Baltz, 1993). 



Teleostean sound production is 

 generally accomplished through one 

 of three mechanisms: hydrody- 

 namic sound production via move- 

 ment through the water, stridula- 

 tion of bony body parts, or the use 

 of specialized drumming muscles. 

 The latter two mechanisms are of- 

 ten amplified by sympathetic vibra- 

 tion of the swim bladder, especially 



in the case of the drumming or sonic 

 muscles. The sonic muscles may be 

 intrinsic or extrinsic to the swim 

 bladder. Intrinsic sonic muscles 

 originate and insert entirely on the 

 swim bladder, and appear as a part 

 of the swim bladder wall. Extrinsic 

 sonic muscles, however, originate on 

 the cranium, pectoral girdle, or lat- 

 eral body wall musculature and in- 

 sert on or near the swim bladder 

 (Tavolga, 1964; Demski et al., 1973). 

 Male sciaenids produce a 'drum- 

 ming' sound through the use of 

 sexually dimorphic, extrinsic sonic 

 muscles. The Atlantic croaker, Micro- 

 pogonias undulatus, is the only 

 member of this family in which the 

 sonic muscles are found in both the 

 male and female (Smith, 1905; Tower, 

 1908; Fish and Mowbray, 1970; Hill 

 et al., 1987). The drumming behav- 

 iors of sciaenid species are primarily 

 limited to the reproductive periods of 

 these species (Fish and Cummings, 

 1972; Takemura et al., 1978; Mok and 

 Gilmore, 1983; Saucier and Baltz, 

 1993). Male drumming in sciaenids 

 is believed to play a role in the spawn- 

 ing behavior of these species 

 (Pearson, 1929; Guest and Lasswell, 

 1978; Thomas 1 ). 



1 D. L. Thomas. 1971. The early life history 

 and ecology of six species of drum 

 (Sciaenidae) in the lower Delaware River, 

 a brackish tidal estuary. Ichthyological 

 Associates, Delaware Progress Rep. 3 

 (Part III), 247 p. 



697 



