90 J. Douglas Oliver 



The two fishes examined were Leptolucania ommata Jordan, the 

 pygmy killifish, and Gambusia affinis Baird and Girard, the mosquitofish, 

 small members of the order Atheriniformes. Leptolucania ommata lives 

 in quiet, densely vegetated fresh waters from southern Georgia and 

 Alabama to Florida (McLane 1955, Laerm et al. 1980). Gambusia 

 affinis is native from southern Illinois to Texas and Georgia, and it has 

 been introduced to warm waters around much of the world, primarily to 

 consume mosquito larvae (Hess and Tarzwell 1942, Krumholz 1948, 

 Hurlbert and Mulla 1981). In marshes on the west side of the Okefenokee 

 Swamp, L. ommata, G. affinis, Enneacanthus gloriosus Holbrook, and 

 Elassoma okefenokee Bohlke are by far the most numerous fishes (in 

 that order at C and R sites, Oliver and Schoenberg 1989). The invididuals 

 used in this study were adults that came within the common distributions 

 of length (L. ommata of 13-20 mm, G. affinis of 15-25 mm standard 

 length). Both species were studied in the field for a 24-hour period in the 

 summer and in the winter. 



The study site is a subtropical marsh that has large daily temperature 

 fluctuations. It lies approximately 200 m E of the entrance to the 

 Suwannee River sill (an earthen dam that borders the west side of the 

 Okefenokee Swamp). This blackwater area (mean depth 43-1 13 cm) had 

 floating and submersed macrophytic vegetation (mainly Nuphar luteum 

 and Utricularia spp.). Daily water temperature ranges were 4-20° C 

 during winter observations, and 26-37° C during summer observations. 

 The site differed from the Okefenokee LCP site of Freeman and 

 Freeman (1985) in that the latter was shallower (10-55 cm) and was 

 dominated by floating, submersed, and emergent macrophytes 

 (Nymphaea odorata, Eriocaulon compressum, and Rhynchospora 

 inundata). 



METHODS 



I obtained evacuation rates by two related methods done 

 simultaneously, which allowed comparison of results (compare with 

 single-method analysis, e.g. Sainsbury 1986). In the "tank" method, the 

 decline in gut contents of fish held without food was converted to an 

 evacuation rate (Staples 1975, Garcia and Adelman 1985). Clear 

 immersed tanks at the edge of the marsh were used to track natural light 

 levels and water temperatures (measured by a standard mercury 

 thermometer). Okefenokee water was filtered into tanks through a 

 screen (<63 mm mesh) to remove potential food items. At approximately 

 4-hour intervals, large fish captured by seine were placed into two tanks 

 and smaller fish into two other tanks, so that the larger fish would 

 neither consume nor frighten the latter. I preserved about half the 

 seined fish immediately in buffered formalin and preserved the rest 



