The Flathead Catfish in Unchannelized and Channelized Missouri River, Nebraska

Flathead catfish, Py10dictus olivaris (Rafinesque), were studied in approximat~ly 83.7 km of unchannelized and 67.6 km miles of channelized Missouri River. Growth rates were slower in the unchannelized section than they were in the channelized section. The oldest fish in the unchannelized section was 25 years old, while in the channelized study area the oldest was 10 years. In the pectoral spines of progressively older fish from both sections, enlargement of the lumen obliterated early annuli. Much of the annual increment of growth was accomplished during June, July and August. Males became sexually mature at 3 to 4 years of age and 350 to 425 mm, while females matured between 3 and 5 years and 350 to 500 mm with most mature females measuring at least 450 mm. Approximately 1,500 eggs per pound of body weight were produced. Three orders of insects (Ephemeroptera, Trichoptera and Diptera) dominated the food habits of young-of-the-year flathead catfish in both study areas; however, there were some generic differences. Yearlings and adults consumed primarily fish and crayfish, with crayfish being more intensively utilized in the unchannelized study area. Fish 200 mm and longer were marked in order to estimate movements and population sizes. Between the two study areas there was little difference in movement patterns. Based on fishermen's reports, 25 percent of the recaptured fish were within 1.6 km from the point of tagging. Mean upstream and downstream distances moved were identical (40.2 km) but 57 percent of the fish were reported downstream of the point of release. Our recapturing of marked fish indicated less movement (86 percent were within 1.6 km) than did recapturing by fishermen because we did not attempt to collect marked fish outside of the two study areas. Marked fish avoided crossing the main channel. Population estimates for fish 200 mm and longer were 17 fish per linear km and 9 per linear km in unchannelized and channelized study areas respectively. Estimated standing crops were 130 grams per hectare in the unchannelized study area and 149 grams per hectare in the channelized study area.