The banded killifish is similar in habitat preference and appearance to the mummichog, "Fundulus heteroclitus", and the two species have been known to interbreed where their habitat overlaps. The banded killifish, while euryhaline, is more commonly found in freshwater, whereas the mummichog primarily inhabits brackish and coastal waters. The two species can be visually identified by the difference in bands; the banded killifish has thin dark bars, while the mummichog has thin light bars. The species can also be differentiated by the thicker caudal peduncle in the mummichog and brachiostegal rays often numbering 6,6 for the banded killifish (5,5 in the mummichog). Banded killifish have larger and more numerous gill rakers compared to mummichogs (8-12 vs. 4-7, respectively).