WENNER ET AL.: LIFE HISTORY OF BLACK SEA BASS 



Reproduction 



Reproductive organs from 6,685 C. striata were 

 resected at sea and fixed in formol-alcohol solution 

 (Humason 1972) or 10% seawater Formalin 4 . After 

 2-6 wk fixation, the tissues were transferred to 50% 

 isopropanol, processed through an Auto-Technican 

 2A Tissue Processor, vacuum infiltrated, and 

 blocked in paraffin. Sections (7 ^m) were cut from 

 each gonad by a rotary microtome, stained with Har- 

 ris hematoxylin, and counter-stained with eosin-y. 

 Histological sections from 300 fishes were read by 

 two observers to develop agreement on sex and 

 maturity stages; the remaining sections were then 

 examined by a single observer. Sex and maturity 

 stages (Table 1) which provided an accurate and ob- 

 jective estimate of reproductive status were modi- 

 fied from Smith (1965), Hilge (1977), and Mercer 

 (1978) to determine size and age at first maturity, 

 spawning season, and sex composition. The stage 

 of gametogenesis and terminology used in gonadal 

 descriptions follow Smith (1965), Combs (1969), 

 Hyder (1969), Moe (1969), Mercer (1978), and 

 Wallace and Selman (1981). 



We included as males not only individuals whose 

 gonads consisted entirely of testicular tissue but also 

 those with functional testicular tissue (as judged by 

 active spermatogenesis) as well as traces of inactive 

 ovarian tissue. Females were defined as either 

 having entirely ovarian gonads or inactive testicular 



4 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Table 1. — Histological criteria used in determining gonadal con- 

 dition of black sea bass, Centropristis striata. 



Gonad class 



Testicular state 



Ovarian state 



Immature 

 Developing 



Ripe 

 (running) 



Spent 

 Resting 



Transitional 



Little or no spermatocyte 

 development. 



A few primary and sec- 

 ondary spermatocytes 

 through lumina filled 

 with spermatozoa. 

 Predominance of sper- 

 matozoa, little active 

 spermatogenesis. 



No spermatogenic activ- 

 ity, some residual sperm 

 present in tubules. 

 Some mitotic regenera- 

 tion of spermatogonia 

 and interstitial tissues. 



Small (<100 /jm) baso- 

 philic oocytes. 



Predominance of oo- 

 cytes with yolk vesicle 

 formation through late 

 vitellogenesis. 

 Late vitellogenesis and 

 presence of hydrated 

 oocytes. 



Unspawned, mature 

 oocytes undergoing 

 atresia. 



Predominance of small 

 basophilic oocytes with 

 residual traces of 

 atresia. 



Inactive or regressing 

 ovarian tissue with con- 

 current testicular prolif- 

 eration. 



tissue in a functional ovary. Transitional gonads in- 

 cluded only those with obviously proliferating tes- 

 ticular tissue within a nonactive, regressing ovary. 

 Simultaneous gonads were those combining equal- 

 ly developed male and female tissue. Immature 

 bisexual gonads were designated as simultaneous 

 juveniles to avoid any implication as to their func- 

 tion at maturity. 



We successfully sexed 80-90% of the fish sampled 

 by histological examination every month but April. 

 More than 75% of those sampled in April were sexed 

 by gross examination of the gonads, and although 

 our determinations of the functional sexes of these 

 gonads were probably correct, the relative occur- 

 rence of transitional and simultaneous gonads in 

 April samples remains unclear. These data were 

 thus used only to complete the seasonal frequencies 

 of functional sexes. 



Gonads from 115 maturing females collected dur- 

 ing April 1979 were removed at sea, split open with 

 a longitudinal incision, and placed in Gilson's solu- 

 tion (Bagenal 1967). Separated oocytes were washed 

 and stored in 70% isopropyl alcohol after digestion 

 of the ovarian tunic and connective tissue and then 

 were decanted into a separatory funnel and diluted 

 to 1 L for enumeration. Three to five 1 mL sub- 

 samples were removed from the suspension, which 

 was well mixed by continuous aeration through the 

 bottom of the funnel. Each subsample was trans- 

 ferred to a petri dish and counted at a magnifica- 

 tion of 10 x . Only ova >0.15 mm in diameter were 

 counted since histological examination of the gonads 

 of maturing and spent females showed only oocytes 

 >0.15 mm developed during the spawning season. 

 Total fecundity was estimated by expanding the 

 mean of the subsamples to the total sample volume. 

 Total fecundity was related to length and weight by 

 standard least squares linear regression (Sokol and 

 Rohlf 1981) and GM functional regression (Ricker 

 1973). 



Mortality Estimates 



Plots of log p frequency on age indicated that 

 black sea bass are fully recruited to commercial 

 traps and hook-and-line gear at age 4, so mortality 

 analysis applies to age 4 and older. The instanta- 

 neous rate of total mortality (Z) was estimated by 

 standard least squares regression (Sokol and Rohlf 

 1981) from the slope of the right descending limb 

 of the catch curve (Ricker 1975). Values of Z were 

 also obtained by converting (appendix I in Ricker 

 1975) rates of survival (S) derived by Heinke, and 

 Chapman and Robson estimates (Everhart and 



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