The harlequin darter is a moderately slender darter with 6 or 7 dark crossbars on the back. The upper lip is often separated from the snout at the midline by a continuous shallow groove. The forward half of the belly lacks scales; the back half is covered by scales of normal size and shape. The gill covers are broadly connected by a membrane across the throat. The lateral line is complete.
The back and upper sides are mottled green. The midside has a series of dark green blotches. The lower parts are yellowish white with scattered dusky spots or blotches. All fins are marked by narrow brown lines and spots. Males are more brightly colored and boldly marked than females.
Similar species: The banded darter is similar, but the harlequin has the second and fourth dark crossbars on the back narrower than the adjacent bars, the body at the base of the tail fin with large blotches, the cheek and gill cover usually without scales, and the pectoral fins very long, extending backward past the tips of the pelvic fins.
Adult length: 1½ to 2½ inches; maximum about 3 inches.
Recorded only from the southeastern lowlands, including tributaries of St. Johns Bayou (Mississippi and Scott counties), and historically from ditches and streams of the Little River system (Dunklin and New Madrid counties).
Habitat and Conservation
Occurs in streams and ditches. This darter prefers sandy bottoms where logs, sticks, and other organic debris are present. It is invariably found in flowing waters, usually where there is noticeable current. In Tennessee, this species avoids small streams and is one of the few darter species taken regularly in the main channel of the Mississippi River.
The diet mostly comprises immature aquatic insects such as midges, blackflies, caddis flies, and mayflies.
State Endangered; a Species of Conservation Concern in Missouri. In our state, this species is known only from streams and ditches of the southeast. Although it also occurs in nearby Kentucky and Tennessee, its limited range and small numbers make it vulnerable to extirpation within our borders.
Spawning probably occurs in February and March, but details of the behavior are unknown. Females are mature at 1 year of age, and the maximum lifespan is at least 4 years. Young harlequin darters hide among finely divided tree roots and in beds of organic debris along the quiet margins of pools. Apparently, harlequin darters migrate seasonally from larger rivers into tributaries during the warmer months.
Darters have been called the “hummingbirds of the fish world” because of the brilliant and varied colors of the breeding males. The next time you admire the colorful fish at a pet store, remember that our own native species possess the same kind of beauty — and that some of them are endangered.
Big fish eat little fish! Darters are midsize predators, consuming nutrients in the form of small insect predators. Their own bodies are in turn consumed by larger predators, such as bigger fish, birds, and others.