The fountain darter is a small fish that does not grow more than 1.5 inches (3.8 centimeters) long. It is reddish–brown in color with a series of dark, horizontal, stitchlike lines along its sides.
Fine specks and dark blotches cover its back. Three dark spots appear at the base of its tail, and dark bars appear below, behind, and in front of its eyes. The black dorsal (back) fin has a broad, red band.
The fountain darter feeds during the day on aquatic insect larvae and small crustaceans, such as crabs or shrimps. It prefers only live, moving prey. The darter remains perfectly still, waiting for its prey to move within 1 inch (2.5 centimeters) of it, then it quickly darts or moves towards its prey (hence its common name, darter).
Female fountain darters can spawn, or lay eggs, throughout the year, but peak spawning takes place in late spring and again in August. After a female lays her eggs on vegetation such as moss or algae, she abandons the nesting site and never returns.
Habitat and current distribution
The largest population of fountain darters is found in a 2–mile (3–kilometer) area of the San Marcos River in Hays County, Texas. A reintroduced population is found in the upper Comal River in Comal County, Texas.
In the mid–1970s, biologists estimated that about 103,000 darters inhabited the San Marcos River. They believe, however, that the current population has increased slightly. The population in the Comal River is thought to be smaller than that of the San Marcos River.
Fountain darters prefer clear, clean water with abundant vegetation along the stream bed. Water temperature of their habitat is usually just above 70°F (21°C).
History and conservation measures
Droughts in the region had forced the Comal Springs, which feed the river, to stop flowing for a time. In 1975, biologists took a number of darters from the San Marcos River and reintroduced them to the Comal River.
Swimmers and other recreational users of the San Marcos River often disturb the algae mats used by the darters for nesting sites. However, the primary threat to the fish is the growing human population in the area and its increasing demand for water.
This demand is depleting the underground aquifer (an underground layer of sand, gravel, or spongy rock that collects water) that feeds the fountain darter’s river habitat.
State and local agencies that manage the use of the aquifer are developing water–use plans to help maintain spring flows to the rivers, and thus save the darter’s habitat.