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Fishery Bulletin 92(4), 1994 



occurrence and intensity of oocyte atresia. For histo- 

 logical preparation, tissue samples were fixed in 10% 

 neutrally buffered formalin for 24 hours, soaked in 

 water another 24 hours, and stored in 70% ethanol. 

 Samples were embedded in paraffin, sectioned to 5— 

 6 (im thickness and stained with Harris' Hematoxy- 

 lin and Eosin Y. Histological classification of ovaries 

 (Table 1) was based on the occurrence and relative 

 abundance of five stages of oocyte development (pri- 

 mary growth, cortical alveoli, partially yolked, ad- 

 vanced yolked, and hydrated) and on the occurrence 

 and intensity of alpha (a) atresia. Terminology for 

 stages of oocyte development and ovarian atresia 

 follows Wallace and Selman (1981), Hunter and 

 Macewicz (1985b) and Hunter et al. ( 1992). 



Fecundity pattern was evaluated through monthly 

 oocyte diameter distributions of fully developed (go- 

 nad stage 3) females collected during the spawning 

 season. Before measurements were taken, oocytes 

 were hydraulically separated from each other and 

 from the ovarian membrane and preserved in 2% 



a) 



a 



1 on 



200 



300 



400 



50 



inn 



poo 



3( 10 



400 



Length class (mm) 



Figure 2 



Percentage of mature male and female At- 

 lantic croaker, Micropogonias undulatus, by 

 10-mm total length intervals, with a logis- 

 tic function (continuous line) fitted to the 

 data. Arrows indicate mean length at first 

 maturity (L 50 ). n=sample size. 



formalin following the method of Lowerre-Barbieri 

 and Barbieri (1993). Oocyte measurements were 

 taken after a preservation period of at least 24 hours. 

 Samples were stirred before oocytes were removed 

 to reduce bias from settling differences caused by 

 oocyte size or density. Oocytes >0.1 mm were mea- 

 sured (±0.02 mm) with an ocular micrometer in a 

 dissecting microscope. Measurements were taken 

 along the median axis of the oocyte parallel to the 

 horizontal micrometer gradations (Macer, 1974; 

 DeMartini and Fountain, 1981). 



To estimate mean length at first maturity (L 50 ) for 

 males and females, the fraction of mature fish per 

 10 mm length intervals was fit to the logistic func- 

 tion by nonlinear regression (Marquardt method), by 

 using the statistical software program FISHPARM 

 (Saila et al., 1988). L 50 was defined as the smallest 

 length interval in which 50% of the individuals were 

 sexually mature. Females were considered sexually 

 mature if they were in gonad stage 2 (developing) or 

 higher (Table 1). However, to avoid classifying rest- 

 ing (reproductively inactive) or early developing fish 

 as immature, and thus obtaining biased estimates 

 of L go , only fish collected in September, when no rest- 

 ing or developing stages were found, were used for 

 this analysis. 



Monthly sex ratios were tested statistically for sig- 

 nificant deviations from the expected 1:1 ratio with 

 a chi-square test (a=0.05). 



Results 



Size and age at maturity 



Atlantic croaker mature at a small size and early 

 age. Males and females started to mature at 170 and 

 150 mm, respectively; at lengths greater than these 

 the percentages of mature fish increased rapidly ( Fig. 

 2). Estimated mean length at first maturity < L 50 ) was 

 182 mm for males (SE=1.46 mm) and 173 mm for 

 females (SE=1.33 mm). For both sexes, all individu- 

 als >250-260 mm were mature. 



The percentage of mature fish by age showed a 

 similar pattern of early maturation. More than 85% 

 of both males and females were sexually mature by 

 the end of their first year and all were mature by the 

 end of their second. 



Spawning 



Spawning of Atlantic croaker in the Chesapeake Bay 

 and adjacent coastal waters extends over a protracted 

 period. Females in spawning phase (gonad stages: 

 fully developed (3), gravid (4), or running-ripe (5); 

 Table 1 ) were collected from July through December 



