Fountain Darter

The fountain darter is known from only two locations, primarily the headwaters of the spring-fed San Marcos River, having been observed as far as 1.25 miles downstream, as well as the upper reaches of the Comal River in central Texas. Its geographic isolation is reflective of its incredibly specific habitation preferences, which demand conditions that can only be found in these two Texas river headwaters. In these unique locations, they can be observed in open areas created by a medium current at depths of 3–5 feet near the outlets of contributing spring heads with rates of flow low enough to retain a layer of percolating sand. These springs can be found adjacent to the main springs that deliver the tremendous volumes of cool, clear water that form each river. They require a stable water temperature, within the low 70s °F, year-round, which the springs provide. The population in the Comal River was extirpated due to spring failure in the 1950s. The current population there is the result of reintroduction in the early 1970s.

The fountain darter feeds on small invertebrates. It breeds all year round, and the eggs are deposited on dead leaves, stems, rocks, algae, or other objects. This fish lives for one to two years.