Northern Studfish

Fundulus catenatus


Northern studfish female, side view photo with black background
Northern studfish, Fundulus catenatus, female
Lance Merry

Fundulidae (killifishes) in the order Cyprinodontiformes


The northern studfish is a sleek, swift topminnow with a slender, elongated shape. Topminnows have a general habit of skimming along just beneath the surface of the water, so the top of the head and forward part of the back are broad and flat, and the mouth is tilted upward so it opens at the upper surface of the head. The body is long, there is no lateral line, and the single dorsal fin is located far back over the anal fin. The tail fin is rounded. None of the fins have spines.

In overall color, the northern studfish has silvery or brownish sides with numerous horizontal streaks and dashes.

Males in breeding condition are among the prettiest of our native topminnows. Males in spawning coloration have electric blue sides with horizontal red lines; their heads and fins are decorated with reddish spots; their paired fins are lemon yellow; their tail fin has a broad orange fringe, often with a black band.


Total length: 6 inches or more. Missouri’s largest topminnow.


Northern studfish male in spawning color, side view photo with black background
Northern Studfish Male in Spawning Colors
Northern studfish, Fundulus catenatus, male in spawning coloration
Habitat and conservation

Prefers moderate or high-gradient streams with rock, gravel, or sand bottoms, and permanent flow of clear water. Most often found in small groups, cruising in shallow water along margins of pools and riffles where there is little current. Most active in morning or late afternoon. Aggressive by nature and adept leapers, northern studfish can leap out of the water with a quick tail flip when attacked.


Although topminnows are famously adapted for skimming and foraging along the water surface, this species seems to feed more from the bottom than other topminnows. Adults mainly eat aquatic insect larvae and snails. Juveniles take more of their food from the surface.

image of Northern Studfish distribution map
Distribution in Missouri

Occurs in the Ozarks and in southwestern Missouri. One of the common and characteristic stream fishes of the Missouri Ozarks, the northern studfish is widely distributed in every principal Ozark stream system except the Neosho. It range has expanded in recent decades, in part due to natural dispersal, but also, in some cases, by bait-bucket introductions.

Life cycle

Lifespan is usually 5 years. Spawning occurs from mid-May to early August. Males guard a territory but do not prepare a nest.

Human connections

Topminnows and other members of the killifish family are generally quite colorful and popular with aquarists.

Ecosystem connections

Just as catfish are specially equipped for hunting along the bottom of the aquatic ecosystem, topminnows hunt in a special zone of water: the water surface, particularly along the shoreline. Both types of fish have adapted to use a part of the aquatic environment other fish don't.