Reproductive Strategies in a Population of Gobiosoma bosci (Osteichthyes: Gobiidae) with Slow and Fast Maturing Individuals

Abstract

The reproductive biology of Gobiosoma boscicollected from November 1986 to October 1987 in the McFaddin Wildlife Refuge in southeast Texas was studied by using morphometric data. Males achieved greater weights per unit length than females, and longevity was about 12 to 13 months. GSI values and mean monthly ovum diameters indicated that the breeding season ran from April to September, with a major activity peak in May and a minor peak in September. Significant differences in male and female standard lengths (SL), ovum diameter, and egg number existed for sexually mature specimens between the first and second peaks of reproductive activity. An egg versus length analysis produced a positive linear relationship. An accessory gonadal structure index (ASGI) was developed and revealed that maximal AGS development corresponded with the male GSI, but did not produce discemable peaks. Two reproductive strategies were followed and depended upon time of hatching and growth rate. Some individuals that hatched early in the breeding season grew rapidly and were capable of egg laying by August or September. Individuals hatched late in the breeding season delayed breeding until the following season. The distribution of the naked goby, Gobiosoma bosci, extends from Long Island, New York, to the state of Carnpeche, Mexico (Hoese and Moore 1977). In view of the markedenvironmentaldifferellces throughout its range, G. boscimay be expectedto vary its reproductive strategies. In a review of life history phenomena, Cole (1954) stated that the age at which reproductionbegins is one of the most significant characteristics, and as such will influence the reproductive success of an individual. Therefore, southerly populations of G. bosci have at least two potential reproductive strategies available to them (Steams and Crandall1984). First, an individual may grow throughout the non-reproduc tive season after hatching and thenengage in breeding during the subsequent breeding season. Alternatively, young-of-the-year may grow rapidly enough to reproduce before the end of the breeding season, and thereby gain a breeding season not available to fish with delayed breeding. As such, individuals within the same populationmay employ one strategy or the other depending upon their time of hatching and environmental conditions. * Corresponding author; current address is Dept. of Biology, Valdosta State University, Valdosta, GA 31698 Gobiosoma bosci, a cavity nester preferring hard substrates (Bechler et al. l99O), has been studiedextensively along the Atlantic Coast. Dahlberg and Conyers (1973), who reviewed much of the literature, postulated that spawning seasons for different populations of G. bosci were variable, and depended on location. They related initiation and termination of spawning to water temperature and indicated peak spawning activity was in the warmest months, May through August. However,they didnot discuss any variations inbreeding strategies. Other reports on G. bosci byNem(lW6),CrabtreeandMiddaugh(l982),and~rnimm and Seok (1989) revealedmany h t s about the life history and ecology of G. bosci. However, none of the above studies examined reproductive strategies of the naked goby -in fthelargest,ClamLake, was the primary siteof this study.