Degree Name

Master of Science (MS)

Semester of Degree Completion

1976

Thesis Director

Leonard Durham

Abstract

Specimens of the steelcolor shiner, Notropis whipplei (Girard) were seined at irregular intervals from Polecat Creek (Coles County, Illinois) from October 1974 to September 1975. Drift and benthic samples were taken in conjunction with fish collections. The stomach contents of the fish were analyzed and compared to organisms found in the drift and benthos. More food taxa were represented in the fish collected during the summer. Aquatic insect forms, primarily chironomid larvae, amounted to 75.6% of the total percentage of foods eaten during the winter as compared to 18.8% for the summer. Adult insects, mainly coleopterans and dipterans, were the major components of the diet in the summer samples. More fish had empty stomachs in the winter (67.3%) than during the summer (8.9%).

Food volumes of different sized fish were found to vary linearly with little difference in percent fullness. The smaller fish ate the smallest foods (ants and chironomids). Medium sized fish ate more algae and aquatic insect larvae while the largest fish ate more of the larger coleopterans and some crayfish chelicerae.

Males and females were found to have differences in their diets. Males ate some different food taxa during the winter. Females had the greatest food volume during the winter. Varying amounts of different food taxa were eaten by each sex during the summer.

Great differences were found between foods eaten and foods available. Ivlev's Index of Electivity was applied to the summer collections and it was determined that the fish selected for terrestrial insect forms. Hymenopterans and coleopterans were found to have high positive Index values. Dipterans (primarily aquatic) were consistently selected against and had low Index values. Electivity was consistent between sexes. Differences in Index values between sexes indicate the possible preference of some food types by each sex. Food consumption may possibly be influenced by availability and density.

Most foods were selected in the same general proportion as they were found in the drift. Evidence exists showing the fish to be surface feeders. Digestion of soft foods was found to be rapid and complete for fish in vitro.

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