Aspects of the Biology of the Spotted Seatrout, Cynoscion nebulosus, in Mississippi

About 3,000 specimens of the spotted seatrout from Mississippi Sound and adjacent water grouped by males and females had a nearly identical standard length (SL) versus total length (TL) relationship, although the equation for males in winter differed from that for those in other seasons. When investigating the SL-weight relationship, some differences occurred both among seasons and between sexes. Therefore, condition coefficients (K) were calculated to compare male and female groups according to their length and state of maturation on a seasonal basis. The hepatosomatic index (HSI) tended to increase with fish length, with relatively high values occurring in winter compared to low ones in summer when livers exhibited an abundance of lipid. Seasonal values of gonosomatic index (GSI) were typically less than those for HSI, except for ripe or nearly ripe fish. Males and females often concurrently exhibited contrasting values for both HSI and GSI. Females matured as short as 189 mm SL and males by 201 mm, and the percentage of gravid females in summer increased with increasing SL. By the time fish reached 40 cm, females constituted 85.7% of the sample from Mississippi Sound, not counting additional samples in 1982 that contained more males between 350 and 475 mm than females. Ovaries contained more oocytes than indicated in the literature. The largest estimate of oocytes over 30 y m in diameter per female was ten and one-half million using a simple volumetric displacement method, or fifteen and one-half million when calculated using a gravimetric technique. Based on histological and other evidence, most individual fish in Mississippi apparently spawned periodically from April to September and even longer during years with appropriate temperature conditions. When gravid, fish tended to group in schools composed primarily of males or females. Tagging studies indicated that neither C. nebulosus nor C. arenarius moved farther than 25 km from their location of release. Both seatrouts hosted parasites that harm the host in natural water and culture conditions, that adversely affect their respective fisheries, and that potentially cause human distress. Several listed parasites had not been reported previously from the fishes. INTRODUCTION The spotted seatrout, Cynoscion nebdosus (Cuvier), supports an important commercial and recreational fishery in the southeastern United States. It constitutes one of the few commercially important fishes in that region that can spawn, develop, and spend its entire life in an estuarine environment. Consumers eat both the flesh and the ripe.roe. Several aspects of the biology of this essentially nonmigrai tory fish that occurs from New York to Mexico depend on the fluctuating salinity and temperature, and, as pointed out by Tabb (1966), details of its biology from different estuaries are needed. Fish from different estuaries apparently spawn in their respective estuary, and few individuals migrate from those areas. Different growth-rates and tagged fish support that premise, as do blood-serum polymorphisms and, to a lesser extent differences in eye-lens proteins. Weinstein and Yerger (1976b) distinguished a separate subpopulation in each of seven estuaries from Texas to the east coast of Florida using electrophoretic methods and showed that the difference in those subpopulations increased with geographic distance. Because evidence favors distinct subpopulations from each estuarine system, because estuaries are vulnerable to environmental alterations detrimental to those subpopulations, and because the biological characteristics of the stock in Mississippi Sound are minimally understood (Etzold and Christmas 1979), this study was undertaken to assess the Manuscript received A p d 7,1982; accepted February 2,1983. Mississippi stock. Most of the data for this study was collected from mid1978 to mid-1980. Atypically low salinity levels over long periods, low temperatures occurring suddenly, and possibly other factors resulted in few available fish during much of the study period. In fact, local fish houses and restaurants had no local spotted seatrout for many continuous months. Nevertheless, collection$ were made and data from these are compared and often combined with previously collected data. I include also some data on tagged and infected C. arenarius Ginsburg, possibly a subspecies of C. regalis (Bloch and Schneider) (see Weinstein and Yerger 1976a). Information on food contents of three seatrout species in Mississippi occurs separately (Overstreet and Heard 1982). References to comparative biological data on C. arenarius are listed by Moffett et al. (1979), and Shlossmanandchittenden (1981) provided the most extensive report on that species. MATERIALS AND METHODS Samples of the spotted seatrout were gill-netted, trammelnetted, seined, or caught by hook and line on a monthly basis from August 1978 to December 1980. Added to data describing those samples are data on fish previously collected for investigations on specific parasites and stomach contents (Overstreet 1977, Deardorff and Overstreet 198 1 , Overstreet and Heard 1982). Those fish not measured, tagged, and released were covered with ice and transferred to the laboratory for detailed analyses. Reliable commercial and recreational fishermen caught some individuals, and Gulf Coast