Feeding Behavior and Developmental, Seasonal and Diel Changes in the Food of the Silverjaw Minnow, Ericymba buccata Cope

Abstract

A study of the feeding behavior and of the developmental, seasonal and diel changes of the food and feeding of the silverjaw minnow, Ericymba buccata Cope, in Vigo County, Indiana, involved the analysis of the stomach contents of more than 1400 fish and some 27 hr of field and laboratory observation. This species is a bottom-feeder relying mainly on taste and tactile senses. Its feeding behavior involves random searching, frequent mouthing of the bottom substrate, jabbing and digging. The intensity and frequency of these activities are influenced by the presence of food and the activity of other members of the school. It feeds throughout the day. The nocturnal food consists mainly of chironomid larvae and the diurnal food, mainly entomostracans. Diptera larvae are the most important spring and summer food, while entomostracans are the most important food in autumn and winter. Smaller fish use a greater volume of entomostracans, a lesser variety of food, and feed more frequently and intensely, while larger fish use a greater volume of Diptera larvae, a wider variety of food, and feed less frequently and intensely. The ecological significance of these findings is discussed. INTRODUCTION The silverjaw minnow, Ericymba buccata Cope, is a common inhabitant of low-gradient, sand-bottomed streams of the eastern United States (Wallace, 1972, 1973a). Wallace (1971, 1973b) studied the growth and reproduction of this species. Hoyt (1970) studied the food of this fish in Kentucky. The present study, conducted in Otter Creek, Vigo Co., Indiana, describes feeding behavior as well as diel, seasonal and developmental changes in the food. METHODS Field collecting.-Specimens were collected biweekly throughout the year in a 4.5-km section of Otter Creek, Vigo Co., Ind. The methods of collecting and the nature of the study area are detailed by Wallace (1972). The studv of the diel changes in food is based on collections taken at 2-hr intervals from 2000 through 0600 hr on 25*26 August 1967 in a 1O0-m stream section of the study area. This site was reasonably homogeneous with respect to, shore vegetation, bottom type, stream depth, current speed and stream width. The fish were initially preserved in 10% formalin and later in 40% isopropyl alcohol. Analysis of stomach contents.-The stomach was removed and placed in the rectangular well (1 mm deep) of a deDression slide, the bottom of which was etched with 1-mm squares. The food was removed, piled tightly to a depth of 1 mm and its total volume estimated