Conservation, Ecology, and Management of Catfish: The Second International Symposium

<em>Abstract</em>.—Little is known about habitat requirements of juvenile flathead catfish <em>Pylodictis olivaris</em>. Previous studies indicate use of coarse substrates associated with riffle habitats in streams; however, limited information on microhabitat characteristics associated with habitat selection exists. To further our understanding of early life history habitat for flathead catfish, we used polyvinyl chloride half tubes (i.e., tubes cut in half longitudinally) of six different diameters (range, 13–76 mm) and depths (range, 25–152 mm) to simulate interstitial spaces provided by coarse substrates and determine (1) whether juvenile flathead catfish selected for interstice size, (2) relative importance of interstitial diameter and depth, and (3) if interstitial space size selection was related to fish body size. A total of 1,316 selection trials regarding interstitial diameter, depth, and the interaction of these characteristics was conducted using juvenile flathead catfish ranging in total length (TL) from 15 to 128 mm. Utilization of interstice diameters and depths was nonrandom (i.e., selection was occurring). Selection of interstice diameter was positively related to fish body size (i.e., total length), whereas all sizes of juvenile flathead catfish most often selected the greatest depth of interstitial space offered. We observed an ontogenetic shift in relative importance of interstice diameter and depth during interaction trials. Flathead catfish less than 40 mm TL selected for interstitial diameter, fish between 41 and 60 mm TL selected for both interstitial characteristics, whereas individuals larger than 60 mm TL selected for interstitial depth. Results of our study are among the first to identify microhabitat-scale characteristics that influence habitat selection by early life history stages of this species.