REPRODUCTIVE BIOLOGY OF 

 THE SPOTTED SEATROUT, CYNOSCION NEBULOSUS , IN SOUTH TEXAS^ 



Nancy Brown-Peterson,^ Peter Thomas,^ and Connie R. Arnold' 



ABSTRACT 



The spotted seatrout, Cynoscion nebulosus, spawns from April through the end of September in 

 shallow bays in South Texas. All females were sexually mature at 300 mm SL and males at 200 mm 

 SL. Histological examination of the testes showed that spermatogenesis began in January and contin- 

 ued until September, although spermatozoa remained in the testes until November. Spermatogenesis 

 was more active in the peripheral lobules of the testes than in the central lobules during the latter 

 half of the spawning season. The sequence and timing of final oocyte maturation (FOM) was investi- 

 gated for the first time in this species. Lipid coalescence began at dawn and germinal vesicle migra- 

 tion started by midmoming. By early afternoon, oocj^tes were hydrated and spawning occurred at 

 dusk. 



Evidence of multiple spawning was examined. Morphological and histological data showed that 

 oocytes were continually recruited from March through the end of September, and the percentages of 

 vitellogenic and fully yolked oocytes did not decline during the spawning season. An average of only 

 15.5% of the vitellogenic oocytes underwent FOM and hydration during a single spawn. Postovulatory 

 follicles were found in many fish with mature ovaries throughout the reproductive season. Laboratory 

 studies showed that this species is capable of repeated spawns. Batch fecundity was best predicted by 

 ovary-free body weight of the fish and averaged 451 ±43 eggs/g ovary-free body weight. Estimates 

 of spawning frequency ranged from every other day to once every three weeks. 



The spotted seatrout, Cynoscion nebulosus , sup- 

 ports important commercial and recreational 

 fisheries throughout its range (Chesapeake Bay, 

 Virginia to Tampico, Mexico; Tabb 1966). 

 Whereas aspects of the reproductive biology of 

 this sciaenid species have been documented 

 throughout its range (i.e., Chesapeake Bay: 

 Brown 1981; Georgia: Mahood 1975; Florida: 

 Moody 1950, Klima and Tabb 1959, Tabb 1961; 

 Mississippi: Overstreet 1983; Louisiana: Hein 

 and Shepard 1979; Texas: Pearson 1929, Miles 

 1950, 1951), a comprehensive study of reproduc- 

 tion in spotted seatrout does not exist for any 

 area. An extensive knowledge of the reproductive 

 life history of a species is necessary to understand 

 certain aspects of its reproductive physiology and 

 endocrinology. Most previous studies have con- 

 centrated on the size at sexual maturity and the 

 extended spawning season of this species (Pear- 

 son 1929; Moody 1950; Tabb 1961; Mahood 1975). 

 A protracted spawning season is generally char- 



iContribution No. 696, University of Texas at Austin, Marine 

 Science Institute, Port Aransas, TX 78373. 



2Marine Science Institute, University of Texas at Austin, 

 Port Aransas, TX; present address; Florida Department of Nat- 

 ural Resources, Indian River Lagoon Aquatic Preserves, 4842 S. 

 U.S. Highway 1, Fort Pierce, FL 34982. 



3Marine Science Institute, University of Texas at Austin, 

 Port Aransas, TX 78373. 



Manuscript accepted February 1988. 

 FISHERY BULLETIN: VOL. 86, NO. 2, 1988. 



acteristic of multiple spawners (Nikolskii 1969). 

 In addition, Overstreet's (1983) histological data 

 suggest that C. nebulosus may be a multiple 

 spawner. However, the possibility that spotted 

 seatrout are multiple spawners has not been thor- 

 oughly discussed in the literature, and previous 

 estimates of fecundity (Sundararaj and Suttkus 

 1962; Overstreet 1983) have not considered the 

 multiple spawning nature of C. nebulosus or have 

 included estimates of batch fecundity. 



In the present study, the reproductive biology 

 of C. nebulosus in South Texas was investigated, 

 and particular attention was given to evidence for 

 multiple spawning and estimates of batch fecun- 

 dity and spawning frequency. The spawning sea- 

 son, spawning sites, time of spawning, and per- 

 centage of running ripe fish were documented. In 

 addition, the temporal pattern of final oocyte 

 maturation was determined. The histological ap- 

 pearance of the gonads was examined, and partic- 

 ular attention was given to the presence of post- 

 ovulatory follicles in ovarian tissue, an indicator 

 of multiple spawning in the northern anchovy, 

 Engraulis mordax (Hunter and Goldberg 1980). 

 The size-frequency distribution of vitellogenic 

 oocytes was examined, since this can indicate 

 multiple spawning (deVlaming 1983). Batch fe- 

 cundity was determined and spawning frequency 



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