For all the fuss about the Watercress Darter, we know very little about it. Some things we know for sure are: It is a small fish, rarely reaching two inches in length. Like all darters, it lacks a swim bladder – a balloon-like organ many fishes have to adjust their buoyancy. This reduced buoyancy helps it rest on the bottom of streams or ponds. The Watercress Darter is particularly fond of habitats where aquatic plants are abundant. It uses this vegetation for hunting, hiding from predators, and reproduction. Watercress darters eat small prey, including tiny snails, aquatic insects, and crustaceans. The fish probably live no more than two to three years.
The fish might be small, but adult males display brilliant colors. Their bellies are bright scarlet or red-orange, as are bands across their dorsal fins and random spots on their sides. In dramatic contrast, the lower fins and additional bands on their dorsal fins are a vibrant turquoise.
As you might expect, these colors help the males attract females for mating. Females want males that are strong and healthy, and those with brighter colors are more likely to be healthier than those with duller colors. Juveniles and females are more prudently shaded, in mottled browns that help them remain hidden.
Little else is known about the fish’s basic biology. Scientific studies of the fish are hampered by its highly endangered status and the difficulty of observing them, due to their small size and tendency to hide in dense vegetation. Ongoing studies are attempting to determine the fish’s habitat preferences and how to improve and protect the species’ habitat.
R. Scot Duncan