Fitzhugh et al.: Reproductive biology of Pogonias cromis in Louisiana 



247 



Seasonal oocyte development 



Ovaries were characterized by dominance of a single 

 population of primary growth (PG) oocytes year-round, 

 with subsequent appearance of more advanced 

 vitellogenic oocytes during the reproductive season. 

 Cortical alveolar (CA (-stage oocytes, signaling onset of 

 development, were first observed in October 1986 

 (Fig. 1). By November, CA and vitellogenic (V) stages 

 were common among females and comprised 4.6 and 

 3.9%, respectively, of the ova counted. We noted in- 

 creasing proportions of CA and V oocytes relative to 

 counts of PG oocytes by December (Fig. 1). Cortical 

 alveolar-stage oocytes peaked during December, and 

 vitellogenic oocytes lagged in time, exhibiting a peak 

 in March (Fig. 1). 



We noted evidence for onset of spawning in 2 fe- 

 males displaying yolk coalescence of vitellogenic oo- 

 cytes during November 1986. We found conclusive evi- 

 dence of active spawning on 16 February 1987, when 

 we detected hydrated oocytes (H) and postovulatory 

 follicles (POF). No fish were caught during January 

 1987 due to bad weather, and there was no evidence of 

 active spawning (i.e., atresia or postovulatory follicles) 

 from samples examined from November, December, 

 or early February (n=61 females). Based on the num- 

 ber of females containing hydrated eggs, spawning 

 peaked in February and March (Fig. 1). Although hy- 

 drated oocytes were not detected in April (Fig. 1), pres- 

 ence of postovulatory follicles indicated some spawn- 

 ing was still occurring (Table 2). Coalescence of 

 vitellogenic oocytes, preceding hydration and ovula- 

 tion, was detected in one female sampled 12 May 1987 

 (Table 2). 



We observed a low proportion of atretic yolked oo- 

 cytes among females during the development phase 

 prior to onset of spawning. These were similar in ap- 

 pearance to atretic oocytes classified by Hunter & 

 Macewicz (1985) as alpha-stage atresia. A low inci- 

 dence of atretic yolked oocytes is considered normal 

 during ovarian development in teleosts (DeVlaming 

 1983). However, we noted an increase in the presence 

 of atretic material as the reproductive season pro- 

 gressed. By 24 April, 13 out of 16 sampled females 

 were classified as atretic state 1, with atretic oocytes 

 <50% of yolked oocytes present. We noted incidence of 

 atretic oocytes >50% of the total yolked oocytes from 

 individuals sampled 12 May 1987, probably signaling 

 a decline in spawning (atretic state 2). By this date, 

 all yolked oocytes were undergoing atresia in 12 out of 

 22 females examined histologically, and all 22 females 

 exhibited some atretic yolked oocytes. By 12 June, 

 atresia of yolked oocytes was complete for all females 

 examined (rc = 19), and only gonadotropin-independent 

 PG oocytes remained (atretic state 3). 



The gonosomatic index (GSI), which is gonad weight 

 expressed as a fraction of body weight, is a common 

 measure of gonad development used to document sea- 

 sonal changes (Nielson & Johnson 1983). We observed 

 a marked peak in GSI for both males and females in 

 March (Fig. 2). Females exhibited the most dramatic 

 change in gonad weight as the season progressed, with 

 mean gonad weight increasing to >8% of eviscerated 

 body weight. Both sexes followed a similar pattern 

 with respect to time of onset, peak, and decline of GSI 

 (Fig. 2). The gonosomatic index corresponded well with 

 histological observations (Figs. 1, 2). Females exhib- 

 ited an increase in GSI above "resting" levels in No- 

 vember, when CA and V oocytes were present. Monthly 

 peaks in GSI during February and March resulted from 

 the presence of hydrated oocytes and an increase in 

 the proportion of vitellogenic eggs. Increased atresia 

 of yolked oocytes observed histologically in April and 

 May, associated with decreased spawning, produced a 

 decrease in GSI (Fig. 2). In June, when all yolked 

 oocytes were atretic, female GSI had dropped to 0.87, 



