Banded Killifish

The banded killifish has a narrow, elongate bluish-gray or olive-colored body with a darker dorsal surface and white or yellowish underparts extending to the anal fin. Spawning males develop yellow pectoral and pelvic fins, a bright blue patch on the anal fin, and brilliant blue iridescence on the lower portion of the body including the area around the anal fin. There are 12–20 vertical bands along the sides. In females the bands usually appear as thin and distinct black bands that often do not span the full width of the body. In males, the bands are silvery in color, are less distinct, and are closer together. The number of bands are useful in sexing an individual; male banded killifish have a greater (approximately >9) number of bands anterior to the dorsal fin. Fins rounded, base of first dorsal ray slightly ahead of or directly over first anal ray.

The banded killifish is widely distributed throughout eastern North America, ranging from the Pee Dee River, South Carolina to Newfoundland; also found in southern Pennsylvania, northeastern Nebraska, and northern Illinois, and north to St. Lawrence-Great Lakes and Mississippi River basins from Manitoba to Quebec. The eastern subspecies is found on the Atlantic Slope, and the western subspecies in the rest of its range. Westward expansion by the eastern subspecies may be the result of introductions as bait or aquarium fish into novel waterbodies, climate change expanding favorable habitat, or a higher pollution tolerance compared to the western subspecies.

Banded killifish have been observed to feed at all levels of the water column. The adults feed on a variety of items such as insects, nymphs, mollusks, turbellarians, and other small crustaceans. Mosquito larvae are also a popular food source. In contrast, the smaller individuals are limited to fewer items such as chironomid larvae, cladocerans, copepods, and midge larvae. Both young and adult banded killifish have been observed to feed mostly in the afternoon.

Adults range from 2 to 3 years in age. Banded killifish are schooling fish, usually traveling in groups of 3–6 individuals, while the juveniles travel in groups of 8–12. The fish are most often found in the shallow and quiet areas of clear lakes, ponds, rivers, and estuaries with sandy gravel or muddy bottoms and with abundant aquatic vegetation. The sand and gravel provides hatchlings and juveniles with places to hide when threatened by predatory fish such as the largemouth bass Micropterus salmoides, northern pike Esox lucius, bluegill Lepomis macrochirus, and trout. Because the banded killifish is small, it generally does not venture into deeper waters, where it would be vulnerable to predation as well as unable to swim in the fast currents. However, adult banded killifish have been observed to travel into deep bodies of water to feed.

Banded killifish are commonly observed to spawn in dense aquatic vegetation because they practice external fertilization where the female lays her eggs that are equipped with adhesive threads that adhere to plants. Spawning occurs from June to mid-August in shallow waters. During the spawning season, the males go through a color change phase. They develop a bright blue patch near the anal fin. In addition, the lower portion of the body changes to a bright blue color.