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

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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 μm 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.

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