Patterns of Morphometric Variation in the Channel and Headwater Catfishes

Abstract

Abstract The purpose of this study was to compare external morphological variation between the headwater catfish Ictalurus lupus and the channel catfish Ictalurus punctatus, and to determine if external characters could be used to improve our ability to identify these highly similar species, as most individuals cannot be identified in the field using available methods. Morphological differences were found between species but were obscured by geographic variation and allometric growth. Overall, headwater catfish tended to be broader, have shorter spines, and have a shorter anal fin base than channel catfish when measurements were adjusted for body size. Fish of both species were broader in New Mexico than their counterparts in Texas; headwater catfish from Mexico tended to be intermediate. A south-to-north cline of decreasing anal ray counts was observed for both species. Each species exhibited similar patterns of allometric growth, with snout and mouth widths and interorbital distances increasing, and len...