FISHERY BULLETIN: VOL, 86, NO. 2 



glacial acetic acid), and vigorously shaken for 30 

 seconds. Within a few minutes the cytoplasm 

 cleared and the germinal vesicle could be easily 

 observed microscopically. Ovarian fragments 

 were taken from females collected at the spawn- 

 ing site over a 24-h period, placed in clearing solu- 

 tion and then examined under low-power magni- 

 fication to determine the stage of final oocyte 

 maturation. 



Oocyte Size-Frequency Distributions 

 and Estimates of Batch Fecundity 



To determine fecundity and the frequency dis- 

 tribution of oocyte diameters, a 2-15 g piece of 

 tissue was removed from the midsection of the 

 ovaries of 57 fish and weighed to the nearest 

 0.01 g. The tissues were placed in a modified 

 Gilson's solution (Bagenal 1966) for 3-12 months 

 and periodically shaken to separate the oocytes 

 from connective tissues. Ovaries containing hy- 

 drated oocytes were examined after three months 

 since hydrated oocytes of spotted seatrout began 

 to disintegrate when left in Gilson's solution for a 

 longer period of time. 



The volumetric method was used to estimate 

 fecundity (Bagenal and Braum 1971). The oocyte 

 samples were suspended in 500-1,500 mL of 

 water and three replicate 0.5 or 1 mL subsamples 

 were taken. All the oocytes >30 ^JLm were 

 counted, and those >80 |jim in diameter (the 

 growing oocytes) in each sample were measured 

 to the nearest 15 ^m using an ocular micrometer. 

 A total of 556-1,110 growing oocytes were mea- 

 sured in each sample. The number of resting 

 oocytes (oocyte diameter 30-80 ^JLm) was deter- 

 mined by diluting the original oocyte suspension 

 1:10, and counting three replicate subsamples. 

 Altogether, the frequency distributions of oocytes 

 from 48 fish were analyzed (3 in developing stage; 

 9 in mature, spawning not imminent stage; 14 in 

 mature, just prior to spawning stage; and 22 in 

 running ripe stage). Fecundity was calculated fol- 

 lowing Macer's (1974) formula and expressed as 

 relative fecundity of number of eggs per gram 

 ovary-free body weight. Batch fecundity (BF) is 

 defined as all oocytes >350 ixm which were 

 undergoing final oocyte maturation that formed a 

 distinct batch, and all hydrated oocytes. This defi- 

 nition of batch fecundity is in agreement with 

 Hunter and Macewicz's (1985) statement that 

 oocytes undergoing final oocyte maturation may 

 be included as hydrated oocytes when hydration 

 occurs very rapidly. 



Spawning of Fish in the Laboratory 



Four female and two male spotted seatrout 

 were maintained in a 30,000 L recirculating sys- 

 tem. The tank, filtration system and feeding 

 regime of the fish has been described previously 

 (Arnold et al. 1976). The salinity ranged from 25 

 to 30%(. Spawning was induced by increasing the 

 temperature and photoperiod from wintertime 

 settings of 13°C, 9L:15D to 26°C and 15L:9D 

 (Arnold et al. 1976). The filter boxes were checked 

 daily for the presence of buoyant, newly fertilized 

 eggs. 



Statistical Analysis 



Simple linear regression, oneway analysis of 

 variance, and analysis of covariance were com- 

 puted for the data using SPSS packaged programs 

 (SPSS 1981). 



RESULTS 

 Size at Maturity 



Some female spotted seatrout were sexually 

 mature after they reached 231 mm SL and >90% 

 of the females had reached sexual maturity at 271 

 mm SL (Table 2). By 300 mm SL, all female spot- 

 ted seatrout were sexually mature. Fish 300 mm 

 SL or larger made up 85.4%, and immature fish 

 comprised 6.5%, of all the females sampled. 



Male spotted seatrout reached sexual maturity 

 at a much smaller size than females. The size at 



Table 2. — Number and percentage of mature female and male 

 spotted seatrout by 10 mm size categories collected in South) 

 Texas, April 1982-N^ay 1985. Maturity was judged by histological 

 and macroscopic inspection. 



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