FISHERY BULLETIN: VOL. 86, NO, 2 



vitellogenic oocytes (Fig. 5) and fecundity esti- 

 mates show that only about 15% of the growing 

 oocytes undergo FOM prior to a spawn. Histolog- 

 ical data shows that the percentage of vitellogenic 

 oocytes in the ovary remains constant throughout 

 the spawning season (Fig. 4), which suggests that 

 new oocytes may be recruited into the vitellogenic 

 phase as rapidly as mature oocytes are released. 

 Convincing histological evidence of multiple 

 spawning is the presence of postovulatory follicles 

 (POF) from May through the end of September in 

 ovaries containing many vitellogenic oocytes. 

 Hunter and Goldberg (1980) characterized pos- 

 tovulatory follicles in laboratory-spawned En- 

 graulis mordax, a multiple spawning fish, and 

 found POF in all females that had spawned in the 

 laboratory one or two days previously. Finally, 

 laboratory studies also show that spotted seatrout 

 are capable of multiple spawning under relatively 

 constant environmental conditions (Table 6). 

 Tucker and Faulkner (1987) also found that six 

 female fish kept in raceways outdoors at the am- 

 bient summer temperature and photoperiod 

 spawned repeatedly. 



Spawning Frequency 



It is especially difficult to determine the 

 spawning frequency of wide-ranging, multiple- 

 spawning marine fishes such as C. nebulosus that 

 are not group-synchronous spawners. One 

 method to estimate spawning frequency is to 

 count the number of distinct batches of vitel- 

 logenic oocytes in the ovary (Shackley and King 

 1977). However, only one distinct batch of vitel- 

 logenic or hydrated oocytes can be distinguished 

 in spotted seatrout ovaries at any one time (Fig. 

 5) and the reliability of this method has been 

 questioned (deVlaming 1983). Therefore, three 

 techniques were used to estimate spawning fre- 

 quency in spotted seatrout. 



Spawning frequency was estimated to be once 

 every 3.6 days from the percentage of running 

 ripe fish caught on the spawning grounds. Al- 

 though this is probably an overestimate owing to 

 sampling bias, the error may not be susbtantial, 

 since the spawning grounds are also the feeding 

 grounds for this species (Moody 1950) and many 

 nonspawning individuals were captured. The 

 time of sample collection did not significantly in- 

 fluence the estimate of spawning frequency. High 

 spawning frequencies were also obtained (every 

 2.3 days) when fish were captured 6-12 hours 

 prior to spawning and examined for signs of final 



oocyte maturation (Table 5). The spawning fre- 

 quency of other sciaenids fishes has been esti- 

 mated by this technique (DeMartini and Foun- 

 tain 1981; Love et al. 1984). Additionally, Hunter 

 and Macewicz (1985) suggested that this method 

 produces a useful first approximation of spawning 

 frequency. 



The proportion of fish having POF in the ovary 

 has also been used to determine spawning fre- 

 quency (Hunter and Goldberg 1980; Albeit et al. 

 1984; Hunter and Macewicz 1985). Spotted 

 seatrout were found to have POF throughout the 

 spawning season, although the age of the POF 

 was often difficult to determine. Furthermore, de- 

 tailed laboratory studies have not been under- 

 taken to accurately age POF in spotted seatrout. 

 However, the once a week estimate of spawning 

 frequency obtained using this method is similar 

 to spawning frequencies reported for two other 

 sciaenids, the queenfish, Seriphus politus, (De- 

 Martini and Fountain 1981) and the white 

 croaker, Genyonemus lineatus, (Love et al. 1984). 

 Spawing frequency estimates from POF are prob- 

 ably more reliable than estimates based on the 

 number of spawning fish since sampling bias 

 is less likely to occur when capturing fish with 

 POF. 



Another method used to quantify spawning fre- 

 quencies in various species is direct observation 

 of spawning in the laboratory or in "controlled" 

 field situations, such as impoundments (Gale and 

 Deutsch 1985; Hubbs 1985; Heins and Rabito 

 1986). Spotted seatrout spawned an average of 

 once every three weeks per individual under con- 

 trolled temperature and photoperiod in the labo- 

 ratory (Table 6). Tucker and Faulkner (1987) 

 found that six female spotted seatrout kept out- 

 doors at ambient temperature and photoperiod 

 averaged one spawn per individual every 2.3 

 weeks. The same spawning frequency was noted 

 for an individual female, although that same in- 

 dividual later spawned three times in four days 

 (Tucker and Faulkner 1987). Thus, spotted 

 seatrout appear to be capable of the high spawn- 

 ing fi"equencies estimated from field-caught fish 

 with hydrated ovaries, although this frequency is 

 probably not sustained throughout the entire 

 spawning season. In general, the spawning fre- 

 quencies in both laboratory studies are lower 

 than those estimated from actual spawning fish 

 in the field. However, it is unclear whether this is 

 due to an overestimation of spawning frequency 

 in the field or to a decline in spawning frequency 

 owing to confinement in the laboratory. 



386 



