The least darter (Etheostoma microperca) is a small, robust freshwater fish found in North America (3). It has a deep, flattened body, a rounded snout, large eyes and an unscaled breast (4). It is olive-brown above and white to yellow on the underside. There is a series of dark blotches along the sides, a distinct black line runs through the snout and eyes, and there is a dark teardrop under the eyes. There is also black spotting on the underside (5).
During the breeding season, the male least darter becomes dark green with iridescent green scales and the dark blotches turn black. The caudal fin and the second dorsal fin become milky white with charcoal grey bands, and the pelvic and anal fins become enlarged and bright orange (5).
- Length: up to 4.4 cm (2)