The fish fauna of the area studied is transitional between the Ozarkian and Great Plains faunas.

Fluctuation in water level seemed especially important in determining distribution of fishes in the area studied. Variable climate characteristic of the region studied causes recurrent floods and intermittency in streams. Both of these conditions have probably been accentuated by man's modifications of the habitat. The effects of intermittency were most strikingly demonstrated in small creeks of the uplands. The number of species of fish in the highly intermittent streams was small—especially in the uppermost pools sampled—but the actual number of fish was often high even though the number of species was low. In several instances the only fishes found in these isolated pools were Lepomis cyanellus and Ictalurus melas. This phenomenon of concentrated numbers of individuals of a few species would indicate the presence of limiting factors that allow only those species most tolerant of the particular factor to flourish.

Soon after rains restored flow in these intermittent creeks L. cyanellus and I. melas appeared in parts of the channels that had previously been several miles from the nearest water. Rapid upstream movements of other species after rains was also noted.

It was impossible to ascertain the precise effects of gradient and bottom-type on distribution, but certain species such as Notropis blennius, Notropis girardi, and Fundulus kansae were taken only in streams with sandy bottoms. Notropis deliciosus and Hybognathus placita were most abundant over sandy bottoms.

The high gradient of upland tributaries in the Flint Hills area produced turbulence and bottoms predominantly of rubble. A fauna of which Etheostoma spectabile and Campostoma anomalum were characteristic existed in these waters while they were flowing. As flow decreased and intermittency commenced, qualitative and quantitative changes in the fish faunas were observed. Gradient did not change during drought, but turbulence did. Because turbulence varies with water level as well as gradient, the effect of gradient on fish distribution ultimately is linked to climate.

Probably the small number of fish taken on the Walnut River in comparison with other eastern Kansas rivers (Verdigris, Neosho) results, in part, from the long-term pollution of the stream noted by Clapp (1920:33) and Doze (1924). No percid fishes, black bass, or madtom catfish were taken on the Walnut in Cowley County and the species of Notropis numbered only three.

Four faunal associations seem to be recognizable in the area.

Arkansas River Fauna

This fauna contained Notropis girardi, Notropis blennius, Hybopsis aestivalis tetranemus, and Fundulus kansae which, in this area, did not seem to wander far from the sandy main stream of the Arkansas. Minnows abounded; Notropis lutrensis and N. deliciosus missuriensis predominated; and Notropis girardi, N. percobromus, and Hybognathus placita were common. In quiet backwaters, coves, and shallow pools Gambusia affinis occurred in great numbers. Lepisosteus osseus seemed to be the most important predator.

Lower Walnut River Fauna

The Walnut River in Cowley County supported large populations of deep-bodied suckers, carp, and gar. Notropis lutrensis and N. percobromus were characteristic minnows. Lepomis humilis abounded at some stations. The fauna of the main stream of the Walnut River was somewhat intermediate between that of the Arkansas River and that of the three streams considered below. Fifteen of the species common to the Big Caney, Elk, and Grouse systems were also taken in the Walnut River main stream. Thirteen species were common to the Walnut and Arkansas rivers. Seven species were common to all these streams.

Caney-Elk-Grouse Main Stream Fauna

This fauna includes fishes living not only in the main streams but also in the lower parts of the larger tributaries of these streams. The fauna was comparatively rich: in the main stream of Big Caney River 39 species were taken, in Grouse Creek 35 species, in the Walnut River main stream 21 species, and in the Arkansas River 19 species. It has been pointed out that large rivers such as the Walnut and Arkansas have been subjected to greater direct and indirect modification by man, possibly resulting in a less diverse fauna than would otherwise occur in these streams. At present, there is a paucity of ecological niches in the upland tributaries and large rivers, as compared with streams of intermediate size. Fishes typical of the Caney-Elk-Grouse association were Notropis umbratilis, Lepomis megalotis, Lepomis humilis, Labidesthes sicculus, Fundulus notatus, and the two species of Micropterus (Micropterus punctulatus was not taken in Grouse Creek).

Upland Tributary Fauna

Tributary faunas were divisible into two categories: (1) Those of the Walnut River and Grouse Creek (intermittency was severe, species were few, with Ictalurus melas and Lepomis cyanellus predominating); (2) those of Big Caney River (stream-flow was more stable, and eastern fishes, some of which have Ozarkian affinities, occurred in greater abundance than in any other part of the area surveyed). In the latter streams Campostoma anomalum and Etheostoma spectabile usually were dominant. Pimephales notatus, Notropis volucellus, N. camurus, N. boops, and N. rubellus characteristically occurred. Notropis lutrensis was sparsely represented in flowing tributaries. Notropis umbratilis, which seems to prefer habitats intermediate between those of Notropis lutrensis and Ozarkian shiners, was usually represented. Deep-bodied suckers and carp were not taken in upland tributaries but Moxostoma erythrurum was common and Minytrema melanops was taken.

The kinds and numbers of shiners (Notropis) taken at different points along Grouse Creek seem significant. N. lutrensis and N. umbratilis occurred throughout the stream but were rare in sluggish areas where populations of Gambusia affinis, Fundulus notatus, and Labidesthes sicculus flourished. At the lowermost station Notropis percobromus and N. buchanani were taken; these were not present in other collections. In the uppermost stations where water remained plentiful, N. boops and N. volucellus were taken, and N. rubellus has been recorded.

In the broader distributional sense those fishes that seemed most tolerant of intermittency (Lepomis cyanellus, Lepomis humilis, Ictalurus melas, Notropis lutrensis) are widely distributed in the Arkansas River Basin, and are common in the western part of the Arkansas River Basin. Species less tolerant of intermittency are Notropis boops, Notropis camurus, Notropis rubellus, Notropis volucellus, and Pimephales tenellus; they have not been taken far west of the area studied, and become more common east of it.