FISHERY BULLETIN: VOL. 71, NO. 1 



are temporary visitors, do not lay adhesive eggs 

 in the shells, and are rarely found in the inter- 

 stices of the reef. 



The oyster association offers advantages to the 

 gobies and other fishes. The reef provides nest- 

 ing sites, food, and added protection from pred- 

 ators. A great diversity of reef invertebrates 

 is available for food (Wells, 1961). G. bosci eat 

 Gammarus and other crustaceans, annelids, 

 small fish, ova (Hildebrand and Schroeder, 

 1928), and dying oysters (Hoese, 1964). They 

 eat brine shrimp in aquariums and probably feed 

 on other zooplankton in nature. Gobiosoma spe- 

 cies may be significant predators in the food 

 chain of an oyster community, but are probably 

 unimportant as prey species unless their eggs 

 are eaten. Hildebrand and Cable (1938) re- 

 ported that eggs of Chasmodes attached in oyster 

 shells were preyed on by the crab Eurypanopeus 

 depressiis. We found three G. ginsburgi in the 

 stomach of Urophycis floridanus. Gobiosoma 

 species are reported in the food of predaceous 

 fishes, including several sciaenids (de Sylva 

 et al., 1962; Darnell, 1958; Hoese, see footnote 

 3) , but their secretive habits would protect them 

 from predation when they occupy reefs. 



SEXUAL DIMORPHISM 



G. bosci and G. givsburgi are sexually dimor- 

 phic in their color, body size, and genital papilla. 



Male G. bosci tend to be darker (Breder and 

 Rosen, 1966), and males were observed to turn 

 darker when they were actively defending their 

 nests. Males reach a larger size than females 

 and are generally larger (Tables 2 and 3) as in 

 G. robustum (Springer and McErlean, 1961). 

 For G. bosci, the largest male and female were 

 50 mm and 37 mm SL (standard length), re- 

 spectively. Corresponding lengths of G. gins- 

 burgi were 41 and 32 mm. Maximum recorded 

 length of G. bosci is 58 mm (Schwartz, 1961). 

 Male G. ginsburgi reach 53 mm total length (42 

 mm SL) (de Sylva et al., 1962). 



The sexes are easily separable by the structure 

 of the genital papilla (Ginsburg, 1933). The 

 papilla of males is triangular and compressed, 

 whereas the papilla of females is conical, fleshy, 

 with a larger opening than in males, and with 

 fingerlike projections around the tip. The pa- 

 pilla is poorly developed in juveniles, accounting 

 for most of the unsexed specimens in Tables 2 

 and 3. The papilla is most developed during 

 the breeding season in G. robustum (Springer 

 and McErlean, 1961). 



Ginsburg (1933) found a predominance of 

 males in collections of G. bosci, G. ginsburgi, 

 and G. robustum and considered this to be pos- 

 sibly due to gear selectivity for the larger gobies. 

 With the exception of collections of guarded 

 nests, there is a relatively even sex ratio in our 

 collections of G. bosci and G. ginsburgi. For 

 example, G. bosci was represented by 20 males 



Table 2. — Monthly length frequencies of Gobiosoma bosci from the Georgia coast, April 1967-June 1970. M - 

 male, F - female, U - sex unknown (including juveniles), I - incubation of eggs or larvae, G - gravid female. None 

 were collected in September. 



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