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



which most male spotted seatrout attain sexual 

 maturity could not be determined, since the 

 smallest fish collected by the sampling methods 

 (200 mm SL) were all sexually mature (Table 2). 



Season and Time of Spawning 



Histological and macroscopic examination of 

 the gonads (see Table 3 and Figure 3) and mean 

 GSI values (Fig. 2) show that spotted seatrout 

 have an extended reproductive season in South 

 Texas. Mean GSI values of males and females 

 increased by April 1982-85 and remained ele- 

 vated through the end of September. A 5°C in- 

 crease in water temperature at the sampling sites 

 to 23°C during the first week of April 1982-85 

 was paralleled by an increase in GSI to 2.1 in 

 males and 4.5 or greater in females. The pattern 

 of seasonal changes in mean GSI values of males 

 was relatively consistent during the three-and-a- 

 half years of sampling. Mean GSI values began to 

 increase in mid-February, reached a maximum of 

 1.9-2.4 by April, and slowly declined during the 

 spawning season until they dropped rapidly to 

 regressed levels of 0.2 by the first half of October 

 (Fig. 2). The seasonal patterns in mean GSI val- 

 ues of females were also similar from 1982 to 



1985. In all four years, mean GSI increased in 

 April and subsequently declined in May. In 1982- 

 84, mean GSI increased again later in the season 

 prior to the final decrease to regressed levels in 

 October (Fig. 2). Thus, mean GSI values appear to 

 be bimodal, with one period of peak spawning 

 activity in April, and the second period of peak 

 spawning activity varying between August 1982 

 and July 1983 and 1984. 



Male and female spotted seatrout in spawning 

 condition (males with freely flowing milt, females 

 with ovulated oocytes) were consistently captured 

 during a 2-h period around dusk over shallow (1 

 m) beds of Thalassia testudinum or Halodule 

 wrightii bordered by a channel 2 m deep. The 

 salinity at the spawning sites ranged from 20 to 

 37%c. Although actual spawning was not ob- 

 served, collection of newly fertilized eggs from the 

 spawning area at dusk confirmed that spawning 

 was taking place (Holt and Holf*). Spawning fish 

 were not captured over beds of scattered H. 

 wrightii or T. testudinum that were not immedi- 

 ately adjacent to a channel. Females with freely 



^S. A. Holt and G. J. Holt, University of Texas at Austin, 

 Marine Science Institute, Port Aransas, TX 78373, pers. com- 

 mun. 1983. 



t 



33 



1-25 

 17 

 1-9 



I I I I I I I I I I I I | ' i '' r V ; 'i^ | "r | T | I M I M ' M 1 M ' I M I I ly'V' I I I I M M I I I Ml I I I I I I I I I ' i ' i ' i 



°C 



MM J SNJMMJ 

 1982 1983 



N J M M' J S N 

 1984 



J M M 

 1985 



Month 



Figure 2. — Bi-monthly mean water temperature and mean gonadosomatic index (GSI) of male and female spotted seatrout collected 

 in South Texas from March 1982 to May 1985, including ± 1 SE of the mean. Sample size for each data point: 3-61 for females (sample 

 size <15 in only 9 cases) and 2-52 for males (sample size <9 in only 9 cases). 



377 



