Morphology and Variation of the American Cyprinid Fishes Chrosomus erythrogaster and Chrosomus eos

Intercharacter correlation coefficients among 24 morphological characters (nine measurements, nine ratios between various body dimensions, and six meristic traits) were derived for samples of the minnows Chrosomus erythrogaster and C. eos from Minnesota, where intergradation between these fishes has been suspected. These analyses did not demonstrate obvious geographic variation in either species and indicated that two distinct morphological types exist. Certain head dimensions are the most useful external characters for distinguishing between species. The snout is comparatively short and the mouth upturned in young specimens of both species. During ontogeny the snout of C. erythrogaster attains a greater length in relation to length of orbit and length of mouth, and the mouth becomes increasingly less oblique. Snout and orbit remain subequal in length throughout life in C. eos, and the mouth remains relatively oblique.