Spottail Killifish

Heterandria bimaculata

Heterandria bimaculata, the spottail killifish or twospot livebearer, is a small freshwater livebearer in the family Poeciliidae. Adults reach about 10 cm (females) and 5 cm (males) with an elongated body showing olive-brown to yellowish coloration. Two distinctive dark spots are present: one at the base of the dorsal fin and one at the caudal base. Males have a modified anal fin (gonopodium) for internal fertilization. This species inhabits freshwater streams, rivers, and springs at depths of 0-3 meters in the highlands of Mexico and Central America, from San Luis Potosi to Honduras. They prefer flowing waters with rocky or gravelly substrates and moderate vegetation. Heterandria bimaculata feed on small insects, algae, and detritus. As livebearers, females give birth to relatively small broods of live young. They are found at higher elevations than most poeciliids, inhabiting cooler mountain streams. Their two distinctive spots and highland habitat make them interesting subjects for freshwater naturalists.