Trophic Ecology of the Frecklebelly Madtom Noturus munitus in the Tombigbee River, Mississippi

Abstract

Aspects of the trophic ecology of the frecklebelly madtom Noturus munitus, from a site on the Tombigbee River, Mississippi, are described. Aquatic insect larvae comprised the bulk of the diet. Noturus munitus differed little in gut content from a group of associated syntopic species. Males and females differed in mean prey length in autumn. Individual trophic diversity increased significantly in the autumn for both sexes and with standard length. Mean prey length and total prey volume did not increase with fish size. INTRODUCTION The mechanism of trophic resource allocation in fish communities may be complicated by ontogenetic, sexual, seasonal and diel differences within individual species. Because of the indeterminate nature of fish growth, changes in food habits that occur with age may be related to aspects of fish morphology and there may be seasonal changes in diet. Numerous studies have reported changes in diet with season and fish length in darters and madtoms (e.g., Turner, 1921; Daiber, 1956; Braasch and Smith, 1967; Page and Smith, 1970, 1971; Page, 1974, 1975, 1980; Mayden and Burr, 1981; Burr and Mayden, 1982). Northcote (1954) related diet changes to increasing size in Cottus. Werner (1974) studied the relationship between optimal prey size and predator mouth size, and variables such as trophic diversity and prey width have been shown to change ontogenetically (Nakashima and Leggett, 1978; Fahy, 1980). However, our knowledge about these relationships is limited for many species. This study focuses on ontogenetic and sexual differences in diet composition, prey size, prey volume and individual diet diversity of the frecklebelly madtom Noturus munitus, a little-studied, nocturnal, benthic species of the Tombigbee River, Mississippi. The numeric and volumetric characteristics of the gut composition are described and seasonal, sexual and size class differences in six attributes of the prey are considered. METHODS AND MATERIALS Specimens of Noturus munitus (N = 116) were collected between December 1979 and February 1980 from a site on the Tombigbee River N of Hwy. 50, 14.5 km NW of Columbus (Lowndes Co.), Mississippi. Specimens were collected between 1900 and 2200 hr at approximately 30-day intervals. Because of flooding, few madtoms were collected between April and early June of 1980. Specimens from the Tulane University Museum of Natural History (N = 43) that were collected at the same site and time of day in 1969 (G. H. Clemmer, pers. comm.) were used to estimate spring diets. Because few specimens were collected in some months, data are analyzed for two seasons, spring (February through July) and autumn (August through December). I obtained no specimens in January. The spring period coincides with the breeding period of the species (Trauth et al., 1981). Each specimen was measured for standard length (Hubbs and Lagler, 1958).