Morphological Models for Identifying Largemouth Bass, Spotted Bass, and Largemouth Bass × Spotted Bass Hybrids

Hybridization is common among many closely related fishes, such as the largemouth bass Micropterus salmoides and spotted bass M. punctulatus. Although these species are common members of the sport fish community in midwestern and southeastern U.S. reservoirs, fairly little is known about their ecological interactions or the potential for the introduction of one species to influence the other species. To address these ecological questions and develop appropriate management strategies, reliable field and laboratory identification of each parental species and their hybrid is required. To that end, we collected juvenile (n = 60) and adult (n = 78) largemouth bass, spotted bass, and largemouth bass × spotted bass hybrids from Lake Norman, North Carolina, a system with a historically strong largemouth bass fishery that recently experienced a spotted bass introduction. We recorded a suite of morphological traits on each individual and correlated those observations with DNA sequences from one mitochondrial marker and three nuclear DNA markers in an attempt to develop morphological field and laboratory methods for identifying individuals of the parental species and their hybrid. After confirming that largemouth bass and spotted bass were hybridizing in Lake Norman, we used classification tree analyses to form dichotomous keys for field and laboratory identification of parental individuals and hybrids at juvenile (50–100 mm total length) and adult (300–500 mm) life stages. These keys should provide fishery biologists and managers with a tool to identify these two species, which commonly interact and closely resemble one another. In addition, these keys should be useful in providing evidence that largemouth bass and spotted bass are hybridizing before more expensive techniques like DNA sequencing are pursued.