The blackspotted topminnow is a sleek, swift fish with a slender, elongated shape. Topminnows have a 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.
This particular species is light brown, with a velvety black longitudinal stripe running from the tip of the snout through the eye to the base of the tail fin. It is distinguished from its cousin, the blackstripe topminnow, by having upper sides with few to many black spots that are regular in outline and that are about as dark as the stripe along the midside.
Total length: 2 to 3 1/2 inches.
Common south of the Missouri River; not present in most of the northern half of the state.
Habitat and Conservation
Along large lowland rivers and in the pools of streams draining flatter uplands. Prefers slightly warmer and more turbid streams than the blackstripe topminnow, so it inhabits streams where the closely related blackstripe topminnow is not found. Widespread and abundant in the Ozark and Lowland regions, wherever there are clear permanent-flowing streams, where it lives in quiet water at the edges of pools or near emergent aquatic plants.
Topminnows cruise along the upper surface of water, looking for invertebrates on the water surface. They feed most intensely in the morning, late afternoon and evening. About half the diet is terrestrial insects; the rest of the diet is aquatic insects, crustaceans, snails and algae (algae passes through the gut undigested).
Spawning occurs in spring. This species lives in pairs or small groups that cruise slowly along the shoreline. They are most active mornings and evenings and commonly live 2 to 3 years.
Topminnows and other members of the killifish family are generally quite colorful and popular with aquarists.
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.