BROWN-PETERSON ET AL.: REPRODUCTIVE BIOLOGY OF THE SPOTTED SEATROUT 



suggesting a prolonged spawning season is a com- 

 mon reproductive strategy among sciaenids liv- 

 ing in temperate and subtropical waters. 



The duration of the spawning season may be 

 related to water temperature. Perhaps this appar- 

 ent association with temperature is related to the 

 viability and development of spawned spotted 

 seatrout eggs. Twenty-three degrees may be the 

 minimum temperature necessary for successful 

 spawning, as indicated by both the failure to cap- 

 ture running ripe fish at lower temperatures and 

 by data from spotted seatrout induced to spawn 

 under laboratory conditions (Arnold et al. 1976; 

 Table 6). However, since spawning ceased in Sep- 

 tember when water temperatures were well 

 above 23°C, possibly a decrease in photoperiod in 

 combination with a decrease in temperature pro- 

 vides the necessary cue for termination of spawn- 

 ing. Hein and Shepard (1979) suggested photope- 

 riod may be an important regulating factor in 

 C. nebulosus spawning. Data from laboratory- 

 spawned spotted seatrout (Arnold et al. 1976) also 

 support this speculation. 



The seasonal pattern of mean GSI values dur- 

 ing the spawning season was relatively consistent 

 for both males and females over the Sj-yr period, 

 1982-85 (Fig. 2). The bimodality of the female 

 GSI data suggests the possibility of two peaks in 

 spawning activity, although the timing of the sec- 

 ond peak varies from year to year, thus demon- 

 strating the need for several consecutive years of 

 data. Bimodal spawning peaks have been previ- 

 ously reported for the species by Hein and Shep- 

 ard (1979) in Louisiana, Stewart (1961) in 

 Florida, and Brown (1981) in Chesapeake Bay, 

 VA. However, mean GSI values should be used 

 with caution when attempting to predict actual 

 peaks in spawning activity (deVlaming et al. 

 1982). 



Fecundity 



Accurate annual fecundity measurements are 

 difficult to determine for multiple spawning 

 fishes with an extended spawning season. Meth- 

 ods of calculating annual fecundity from mea- 

 surements of the total number of growing oocytes 

 at the beginning of the spawning season (Bagenal 

 1966), or other approaches based on the total 

 number of oocytes at the beginning of the spawn- 

 ing season minus egg retention at the end of the 

 spawning season (Conover 1985), are inappropri- 

 ate for multiple spawning species such as spotted 

 seatrout which show continuous recruitment of 



oocytes during the reproductive season. Thus, the 

 previous estimates of annual fecundity in spotted 

 seatrout, which did not take continuous recruit- 

 ment of oocytes into consideration and measured 

 either total fecundity (Overstreet 1983) or fecun- 

 dity of growing and vitellogenic oocytes (Sun- 

 dararaj and Suttkus 1962), probably underesti- 

 mated annual fecundity. Furthermore, BF has 

 not previously been calculated for this species. 



Although no monthly differences in BF were 

 apparent (Table 4), sample sizes were too small to 

 draw any definite conclusions from these data. 

 The relatively low coefficient of determination 

 (0.56) is similar to values reported by Conover 

 (1985) for Atlantic silversides, Menidia menidia, 

 another multiple spawning species. Perhaps a 

 more accurate estimate of annual fecundity than 

 previously reported for spotted seatrout can be 

 obtained by multiplying BF by the number of 

 spawns during the reproductive season. Unfortu- 

 nately, as discussed later, estimates of spawning 

 frequency vary considerably, so it is not possible 

 to make an accurate estimation of the annual fe- 

 cundity. However, available data indicate that 

 average annual fecundity may be greater than 10 

 million eggs. 



Multiple Spawning 



Histological examination of the testes revealed 

 that spermatogenesis ceased earlier in the central 

 lobules, although they contained spermatozoa 

 one-and-one-half months longer than the periph- 

 eral lobules. It is possible that the same central 

 lobules act as storage areas for spermatozoa pro- 

 duced by the more spermatogenically active pe- 

 ripheral lobules during the second half of the 

 spawning season, as suggested by Hyder (1969) 

 for Tilapia . This may represent a strategy in mul- 

 tiple spawning fish with a prolonged spawning 

 season that allows for a constant supply of sper- 

 matozoa while investing a minimal amount of en- 

 ergy into spermatogenesis. 



Several lines of evidence indicate that female 

 C. nebulosus also spavni several times during the 

 reproductive season. The relatively high percent- 

 age of running ripe females, fish undergoing 

 FOM and partially spent fish captured through- 

 out the spawning season, and the absence of com- 

 pletely spent fish until the last third of the spawn- 

 ing season, suggest that an individual does not 

 spawn all the vitellogenic eggs in the ovary at one 

 time. Indeed, oocyte size-frequency analysis 

 shows a continuous distribution of growing and 



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