Reductions in cold-water habitat owing to anthropogenic stressors are focusing attention on indicator fish species. We investigated an apparent range expansion in Connecticut of a native cold-water fish, Slimy Sculpin (Cottus cognatus). Unexpectedly, genetic and morphological analyses identified the new population as a non-native cottid from the Ozark region, the Knobfin Sculpin (C. immaculatus). This is the first record of C. immaculatus outside of its native range. The new occurrences were not recognized for over a decade despite comprehensive watershed inventories by state natural resource managers. The mechanism by which the non-native Knobfin Sculpin first arrived in Connecticut is currently unknown. Our findings suggest that unintentional species introductions may occur more frequently than is currently recognized and highlight the need for more comprehensive assessments of non-native species distributions.

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