The third group is composed of channel catfish, flathead, and freshwater drum. This group represents that element of the population that responded most quickly to the resumption of continuous flow. The fact that adult channel catfish and flatheads live in pools and do not require flowing water to spawn gives these species a survival advantage as well as a reproductive advantage over obligatory riffle fishes (such as most darters) in the highly variable conditions found in Kansas streams. These factors resulted in unusually high reproductive success in 1957. Subsequent survival of fry was excellent; however, some mortality in the highly-dominant 1957 year-class became apparent in the 1958 and 1959 collections, accounting for a numerical decline in these species. The ability to respond immediately to increased flow is an adaptive feature that allows these species to maintain high levels of abundance in the highly fluctuating streams of Kansas. The continuous flow that occurred in 1957 in the Neosho and Marais des Cygnes rivers, for the first time in four years, provided the necessary habitat for survival of young catfish hatched in that year. The nearly complete absence of other species on the riffles, and the abundant populations of riffle-insects that I observed in the summer of 1957, were undoubtedly factors contributing to the survival of young. The decrease in abundance of the red shiner may be partially due to an increase in the numbers of other species that are well adapted to conditions of permanent flow. At the completion of my study, the red shiner was still the most abundant minnow in both rivers. In 1957 this species was common in many habitats, including swift riffles, that were later occupied by madtoms, darters, the gravel chub, mountain minnow and sucker-mouthed minnow. The basic pattern of change was clearly an increase in the species that are characteristic of permanently flowing waters, and a decrease in the species that are characteristic of ponds or small, clear streams. PLATE 26 [Illustration: FIG. 1. Neosho River, Middle Station, Sec. 3 and 4, T. 24 S., R. 17 E., looking upstream, July, 1958.] [Illustration: FIG. 2. Neosho River, Lower Station, Sec. 16, T. 29 S., R. 20 E., along gravel bar, July, 1959.] PLATE 27 [Illustration: FIG. 1. Marais des Cygnes River, Upper Station, Sec. 12, T. 17 S., R. 17 E., looking downstream, June, 1960.] [Illustration: FIG. 2. Marais des Cygnes River, Middle Station, Sec. 6, T. 17 S., R. 20 E., looking downstream, June, 1960.] PLATE 28 [Illustration: FIG. 1. Electrical fishing gear used at night.] [Illustration: FIG. 2. Pool at the upper Neosho station in which rotenone was used, Sec. 33, T. 15 S., R. 8 E., looking downstream, June, 1960.] PLATE 29 [Illustration: FIG. 1. Area 1, upper Neosho station, Sec. 33, T. 15 S., R. 8 E., looking upstream, June, 1960.]