There are approximately 41 freshwater, brackish and marine Topminnow species within four genera established in Canada, the United States and Mexico. Despite the name, Topminnows are not closely related to the Minnow family (Cyprinidae). Some Topminnows are commonly referred to as “Killifish,” and these terms are generally interchangeable.
Killifish are characterized by a round body, flattened back and head, and an upturned mouth. The dorsal and anal fins are farther back on the body than on other fishes. The dorsal fin originates a little farther ahead of the anal fin.
Banded Killifish (Fundulus diaphanus), also called “Killies,” inhabit the surface portions of freshwater and coastal marine environments. In Pennsylvania, the Banded Killifish has been recorded from all Pennsylvania watersheds except the Genesee River watershed. They are often used as baitfish for other species.
The Banded Killifish has an elongated body with flattened sides and large, round scales. Both males and females have dark vertical lines on the sides. Lines near the tail are shorter than those on the body. The back is olive, yellowish olive, or brownish yellow, fading to yellowish white or silvery-white on the bottom. The fins are light-olive or yellowish olive.
Killifish have no lateral line, and the tail is squarish. The Banded Killifish has rows of small, sharp teeth in the upper and lower jaw. Adults are usually two to four inches long.
In Pennsylvania, Banded Killifish prefer the quieter portions of still water and slower-moving areas of streams. When small groups of Banded Killifish live in areas of sandy or fine-gravel bottoms, they dig into the bottom when threatened. Larger schools of Banded Killifish show less of a tendency to bury.
Killifish spawn in water of about 70 degrees. The male chooses a site and defends it against other males and intruders. As the male pursues a female, the female emits one egg, which stays attached to the female’s body by a fine strand. When the male pursues the female even more persistently, they come together and the female then emits up to 10 eggs, which also stay attached for a short period. The eggs then fall to the bottom. The spawning pair separates, and when the female moves off, the male pursues her again. This behavior continues until some 50 eggs are deposited in about five minutes. Neither the male nor the female guards the nest or the eggs, which hatch in about three days.
Killifish feed at the surface, midwater and near the bottom on midge larvae and insects. The larger fish consume insects, mollusks and worms.