Food Habits of the Southern Channel Catfish (Ictalurus Lacustris Punctatus) in the Des Moines River, Iowa

Abstract

The stomach contents of 912 channel catfish (769 containing food) taken in a short section of the Des Moines River from September, 1940, to October, 1941, are analyzed. The physical and biotic characteristics of the study area are described; a partial list of the fishes present together with comments on their importance and relative abundance is included.The channel catfish is omnivorous, as is revealed by a review of the pertinent literature and by this study. A wide variety of organisms is eaten (some 50 families of insects alone are represented–these are listed). Insects and fish serve as staple foods, plant seeds are taken in season, and various other items are eaten in limited numbers. The principal groups of foods (insects, fish, plants, and miscellaneous) are analyzed volumetrically, by frequency of occurrence, and numerically.In the area studied, catfish grow at a rate of about 4 inches a year during the first 3 years of life (determined by length‐frequency analysis). These natural size groups are utilized to establish the relationship between size and food habits. Young fish feed almost exclusively on aquatic insect larvae–chiefly midges, blackflies, mayflies, and caddis flies. In fish from 4 to 12 inches long insects continue to make up the bulk of the food, but at progressively greater size larger insects (mayflies and caddis flies) are eaten with increasing frequency and dipterans are of less importance than in the smaller size group; small fish and plant seeds become significant items of diet. In catfish more than 12 inches long, fish and large insects are of major importance, but many seeds and other items are taken. Although fewer insects are eaten by larger fish, those taken are more diversified and include a higher percentage of terrestrial forms.Plant foods, chiefly of terrestrial origin, show the most striking seasonal trends of any of the food organisms. Seeds of the American elm in particular are taken in great numbers in May and June. Terrestrial insects are seasonal in appearance, being eaten at times of the principal flights. Aquatic dipterans are consumed consistently and in large numbers in the spring but progressively less frequently during the summer and fall; Trichoptera, however, are infrequently eaten in the spring but are of increased incidence in the summer and fall. These trends reflect changes in the numbers of organisms available. The numbers of the various species of forage fishes consumed are closely correlated with their relative abundance in the area. Several organisms which have been reported as important foods by other investigators (filamentous algae, microcrustaceans, crayfish, mollusks) are taken in insignificant quantity here, probably because these are rare in the Des Moines River.In periods of low, relatively clear water, forage fish are eaten in sharply increased numbers–a reflection of their greater vulnerability. Feeding appears to be most active during the period from sundown until about midnight. Between 50° and 94° F., temperature does not seem to inhibit feeding, but in the winter the fish rarely feed. The available evidence indicates that adults do not feed during the breeding season.In normal years reproduction of channel catfish is highly successful in prairie rivers. Efforts to increase production should be directed toward improvement of food supply and shelter facilities.