Consumption Rates, Evacuation Rates, and Diets 



of Pygmy Killifish, Leptolucania ommata, and 



Mosquitofish, Gambusia affinis (Osteichthyes: Atheriniformes) 



in the Okefenokee Swamp 



J. Douglas Oliver 1 



Institute of Ecology, University of Georgia 



Athens, Georgia 30602 



ABSTRACT. — I studied feeding dynamics of Leptolucania ommata 

 and Gambusia affinis in the Okefenokee Swamp. Both fishes mainly 

 ate insect larvae (such as Chironomidae) and Cladocera. Evacuation 

 rates ranged from 0.143 (L. ommata in winter) to 0.279/ hour (L. 

 ommata in summer). Daily food consumption (dry weight) ranged 

 from 24.2 (L. ommata in winter) to 148.3 mg/g/day (G. affinis in 

 summer). Maximum consumption by both species was estimated at 

 26.31 mg/m 2 /day, in summer. These values are consistent with other 

 observations supporting a hypothesis that invertebrate prey production 

 is substantial in these blackwater wetlands. 



Relatively little is known about the diets and feeding dynamics of 

 fishes of freshwater wetlands (Weller 1981). Studies of the diets of 

 wetland fishes have concerned those in salt and estuarine marshes (e.g. 

 Harrington and Harrington 1961, Wetzel 1971, Kjelson et al. 1975). I do 

 not know of a previous study on consumption or evacuation rates of 

 any fish in any saltwater or freshwater wetland. 



This study was based on field data from the Okefenokee Swamp, 

 Georgia-Florida, the largest entirely freshwater wetland in the United 

 States (1800 km ). My objectives were to determine the diets and rates 

 of consumption and evacuation under field conditions of two of the 

 most abundant fishes in a marsh on the west side of the Okefenokee 

 Swamp: that is marsh C, the "Control" marsh of Stinner (1983) and 

 Oliver and Schoenberg (1989). To quantify dynamics at the ecosystem 

 level and to estimate minimum invertebrate prey production, I then 

 used measures of daily food consumption to estimate area-based 

 consumption (consumption per m 2 ) by these fish. These invertebrate 

 production estimates may help to resolve whether blackwater habitats 

 have low secondary productivity, as suggested for tropical blackwaters 

 (Janzen 1974, Fittkau et al. 1975, Araujo-Lima et al. 1986), or substantial 

 productivity (Freeman and Freeman 1985). Methods are field-based to 

 obviate elaborate laboratory feeding studies and to obtain data under 

 natural conditions. 



1 Present address: Bureau of Aquatic Plant Management, Florida Department of Natural 

 Resources, 3917 Commonwealth Boulevard, Tallahassee, FL 32399. 



Brimleyana 17:89-103, December 1991 89 



