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



peared similar to the oocyte distribution in non- 

 spawning fish (Fig. 5B, D). The percentage (21%) 

 of growing and vitellogenic oocytes in the ovary 

 remained constant throughout the reproductive 

 season in fish in the mature and running ripe 

 stages. 



Final Oocyte Maturation 



Final oocyte maturation (FOM) was highly syn- 

 chronized in spotted seatrout and occurred only in 

 oocytes >400 ixm ^. Figure 6A shows a photomi- 

 crograph of a histological section of a spotted 

 seatrout ovary in the mature reproductive stage 

 that was not undergoing final oocyte maturation. 

 Many oocytes were in the yolk globular stage and 

 appeared to be fully grown. The first readily ob- 

 servable stage of FOM in "cleared" oocytes was 

 lipid coalescence (Fig. 6B). The oil droplets in the 

 oocytes began to coalesce around the germinal 

 vesicle (nucleus) and subsequently formed one to 

 three large oil droplets. This stage was not always 

 observed in histological preparations since many 

 of the oocytes were not sectioned through their 

 centers. The yolk globules remained discrete dur- 

 ing lipid coalescence. After the lipids had coa- 

 lesced, the germinal vesicle (GV) began to mi- 

 grate to the periphery of the oocyte (germinal 

 vesicle migration, or GVM). GVM could be seen 

 in both histological sections (Fig. 6C) and in 

 "cleared" oocytes (Fig. 6D). The oil droplet occu- 

 pies the center of the oocytes shown in Figure 6C, 

 D. Histological observation of this stage (Fig. 6C) 

 showed that the yolk globules were not coalesced, 

 the oil droplets had coalesced to form one or two 

 large droplets and the GV had begun to lose its 

 integrity and often appeared semicircular. At the 

 completion of GVM, the nuclear (germinal vesi- 

 cle) membrane broke down (GVBD) and the nu- 

 clear material intermingled with the cytoplasm of 

 the oocyte. Hydration occurred shortly thereafter, 

 followed by ovulation and spawning of the fully 

 mature oocyte. 



Final oocyte maturation occurred within 10 

 hours in spotted seatrout in the natural environ- 

 ment (Fig. 7). A total of 209 fish were collected 

 over eight 24-h periods from April through Au- 

 gust in 1984 and 1985. Forty-three percent of the 

 fish collected between the hours of 0500 and 1500 

 were undergoing FOM. Lipid coalescence was 



first observed at dawn (0545), and GVM started 

 at 0900. By 1430, all fish undergoing final matu- 

 ration had hydrated oocytes and ovulation and 

 spawning commenced at dusk (1830) and contin- 

 ued until 2100. None of the fish collected from 

 2100 to 0500 were undergoing FOM. 



Batch Fecundity 



The significant positive relationship {P < 

 0.001) between BF and ovary-free body weight 

 can be best described by the following equation: 

 BF = 459WT - 56,066, r^ = 0.56 (Fig. 8), while 

 curvilinear equations best described the relation- 

 ship between BF and SL and TL. The coefiicients 

 of determination in all cases were <0.56. 



A one-way analysis of variance showed that 

 mean BF (number of eggs per gram ovary-free 

 weight) did not vary significantly during the 

 April through September spawning season. Mean 

 relative batch fecundity was highest in Septem- 

 ber, lowest in May, and varied little during April, 

 June, and July (Table 4). 



A prominent batch of oocytes was present only 

 in females that were in all stages of final oocyte 

 maturation or were running ripe (Figs. 5C, D; 7). 

 The average batch size calculated from 14 fish 

 containing hydrated oocj^es and no postovulatory 

 follicles was 451 ± 43 eggs/g ovary-free body 

 weight. This number averaged 15.5 ± 2.5% of the 

 number of growing and vitellogenic oocytes in the 

 ovary. 



Table 4. — Monthly mean batch fecundity 

 expressed as number eggs/g ovary-free 

 body weight of spotted seatrout in South 

 Texas. All means were not statistically dif- 

 ferent. 



5A 400 (xm live oocyte equals a 350 ^.m oocyte preserved in 

 Gilson's solution. Both measurements represent oocytes begin- 

 ning FOM. 



Spawning Frequency 



To estimate the spawning frequency of spotted 

 seatrout in South Texas, the percentage of run- 

 ning ripe females captured monthly from April 

 through the end of September in 1982 through 

 1985 was examined. Only fish captured at dusk 

 and >305 mm SL were included in this analysis. 

 The percentage of spawning females ranged fi-om 



381 



