Montana Field Guide

Northern Redbelly Dace - Phoxinus eos

The northern redbelly dace is another of Montana's small minnows. This native fish is found in small, clear, plains streams and ponds. During the spawning season, this species becomes quite colorful with red flanks. Its maximum size is about 3 inches. In some locations in the northern U.S. and Canada, the northern redbelly dace hybridizes with its close relative, the finescale dace. The resultant hybrids are very unusual in that they are all females and produce offspring that are likewise all female. Eggs from the hybrids are "fertilized" by the sperm of northern redbelly dace. It appears that this "fertilization" is necessary for egg development to begin, but curiously none of the genetic traits of the male are incorporated into the fertilized embryo. This type of reproduction is known as gynogenesis and is found in only a few fish and amphibians. Here in Montana we have the northern redbelly dace and the hybrids, but no finescale dace. Because of its genetic uniqueness, the northern redbelly dace x finescale dace hybrid is a Fish of Special Concern in Montana.

The northern redbelly dace is olive to dark brown above; the lower side and belly are yellow or silvery except on adult males during summer when the lower side is red. The side has two dark stripes with a light band between them; the upper stripe often breaks into spots toward the tail. The lower stripe is broader and extends from the snout to the base of the tail fin where it may end in a spot. These two lateral stripes are sometimes connected by a dark, oblique line or crossband. The eyes are large. The body is almost round in cross section. The front of the dorsal fin is behind the front of the pelvic fins. The lateral line is incomplete and not distinct and there are no barbels.

Montana Range

Northern redbelly dace prefer clear, cool, slow-flowing creeks, ponds and lakes with aquatic vegetation, including filamentous algae.

Northern redbelly dace eat diatoms and other algae as well as minute animals found in plankton and bottom ooze.

This species is sexually mature at 1 year and spawns May through August. Females may spawn twice each year. Incubation is 8 to 10 days at 70 to 80 degrees F. (B71BRO01).