|Listed||October 13, 1970|
|Description||Tiny, reddish brown darter with dark horizontal lines on the side.|
|Habitat||Clear, quiet waters.|
|Food||Insect larvae, small crustaceans.|
|Threats||Aquifer depletion, dam construction, recreational use of habitat.|
The fountain darter, Etheostoma fonticola, is the smallest species of darter, usually less than 1 in (2.5 cm) in length, and is mostly reddish brown in life. The scales on the sides are broadly margined behind with dusky pigment. The dorsal region is dusted with fine specks and has about eight indistinct dusky cross-blotches. A series of horizontal stitch-like dark lines occur along the middle of the sides, forming an interrupted lateral streak. Three small dark spots are present on the base of the tail and there is a dark spot on the gill cover. Dark bars appear in front of, below, and behind the eye. The lower half of the spinous dorsal fin is jet-black; above this appears a broad red band, and above this band the fin is narrowly edged with black. Male fountain darters differ from females in four morphological characters: banding pattern, spinous dorsal fin coloration, genital papillae, and pelvic and anal fin nuptial tubercles.
Although the fountain darter has been characterized as the most advanced darter, the basis for this was an analysis of a very limited subset of traits, which appear to be highly influenced by environmental factors, such as temperature. The subgenus Microperca, to which E. fonticola belongs, is still thought to be the most derived (specialized) sub-genus of Etheostoma. The evolutionary history of this group is presumed to involve an early separation of the presently recognized E. proeliare and E. microperca groups followed by a later isolation of a subset of an E. proeliare -like ancestor. This E. proeliare -like ancestor survived and became the presently recognized E. fonticola in only the San Marcos and Comal Rivers.
Based on percent frequency of occurrence of food items in fountain darter stomachs sampled from the San Marcos River, juveniles and small fountain darters feed primarily on copepods; medium-sized feed mainly on dipteran and ephemeropteran larvae, and fully mature darters prefer ephemeropteran larvae. Food habit studies are currently underway for fountain darters in the Comal ecosystem.
Food habits of fountain darters in Spring Lake differ from the food habits of darters in the San Marcos River. Casual observations indicate that the overall invertebrate community in Spring Lake is different from the community in the river, which could explain the observed differences in food habits of darters in these two areas on the basis of availability of food items.
Fountain darters feed primarily during daylight and demonstrate selective feeding behavior. Those held in an aquarium feed on moving aquatic invertebrates while disregarding immobile ones, suggesting that these darters respond to visual cues.
E. fonticola are headwater darters that breed in the relatively constant temperature of the San Marcos River. It has been recorded that fountain darters appear to spawn year-round and that the parents, after depositing eggs in vegetation, provided no further care to the young. After hatching, the fry were never free-swimming, due in part to the reduced size of their swim bladders. As in other darters, fountain darter eggs attach to moss and to algae and these eggs hatch in aerated aquaria. Breeding males display nuptial coloration and develop nuptial tubercles on their pelvic and anal fins. Tubercles on darters are thought to stimulate gravid females or to assist in maintaining the spawning position within the vegetation.
Natural populations of fountain darters have two temporal peaks of ova development, one in August and the other in late winter to early spring. Therefore, fountain darters apparently have two major spawning periods annually. The monthly percentages of females with ovaries containing at least one mature ovum also demonstrate the two annual spawning peaks. However, females containing at least one mature ovum have been collected throughout the year, further suggesting year-round spawning. The ovary weight/body weight relationship and the testis width/square root of total length relationship also indicate the two peak spawning periods.
Most darters spawn in the spring or early summer. However, populations of E. lepidum and E. spectabile, which live in areas with slight annual water temperature variation, extend their breeding periods considerably (up to 10-12 months). The extension of the breeding season of E. spectabile throughout the summer is also known for a population inhabiting the Guadalupe River below Canyon Reservoir where releases from the bottom of the reservoir moderate water temperatures, especially during summer months. Since E. fonticola also lives in a relatively constant temperature environment, it is not especially surprising to find that this species spawns throughout the year.
The fountain darter requires: 1) undisturbed stream floor habitats (including runs, riffles, and pools), 2) a mix of submergent vegetation (algae, mosses, and vascular plants) in part for cover, 3) clear and clean water, 4) a food supply of living organisms, 4) constant water temperatures within the natural and normal river gradients, and 5) most importantly, adequate springflows.
In general, E. fonticola prefers vegetated stream-floor habitats with a constant water temperature. Higher densities of the fish are found in mats of the filamentous green algae (Rhizoclonium sp.) and the moss Riccia. It is occasionally found in areas lacking vegetation. Fountain darters have also been observed among leaf litter in the Comal River
Critical habitat has been designated for the fountain darter as "Texas, Hays County; Spring Lake and its outflow, the San Marcos River, downstream approximately 0.5 mi (0.8 km) below Interstate Highway 35 bridge." A field identified of the downstream boundary is the defunct U.S. Geological Survey stream gauge.
The historic range of the fountain darter included the sources, headwaters, and sections of the San Marcos and Comal Rivers in south-central Texas. Today, the fountain darter is found in the San Marcos River from Spring Lake (Hays County) to an area between the San Marcos wastewater treatment plant outfall and the confluence of the Blanco River. The fountain darter is also found virtually throughout the Comal River to its confluence with the Guadalupe River; the species had been previously eliminated from the Comal River when its habitat was reduced to isolated pools by excessive water removal, but reintroduction efforts were successful, and an established reproducing population now occupies the entire Comal aquatic ecosystem from Landa Lake to the vicinity of the Comal/Guadalupe River.
From 1974 until 1981 a stock of fountain darters taken from the San Marcos River near the Interstate Highway 35 crossing was cultured at the federal facility at Dexter, New Mexico, to ensure against a catastrophic loss of the species. This stock has since been discontinued; however, a new culture was established at the San Marcos National Fish Hatchery and Technology Center, now part of the National Biological Service, in 1988.
A 1993 study estimated the San Marcos River fountain darter population (excluding Spring Lake) to be 45,900. Over the past two decades, there has been a real decrease in fountain darter numbers in the San Marcos. 1976 estimates for the same area estimated a population of about 103,000 fish. A 1991 scuba-aided underwater survey of Spring Lake estimated at least 16,000 fountain darters at the springs openings and another 15,000 in the green algae habitat. A 1990 sampling of seven transects in Landa Lake and the Comal River reported a population estimate of about 168,078 darters above Torrey Mill Dam.
Actions that threaten the fountain darter include the destruction of aquatic vegetation in Spring Lake and the San Marcos River, recreational use of the San Marcos River, and long-term water depletion from the Edwards Aquifer. Swimmers and divers disturb the algae mats used by the darter for spawning, and the aquifer, which is part of a vast underground water system, supplies the water needs of more than one million people throughout the region, including the city of San Antonio. A dam on the lower portion of the San Marcos River apparently eliminated fountain darter habitat in that section of the river.
The Texas Department of Water Resources forecasts that groundwater pumping for human uses will continue to increase well into the twenty-first century. At the current rate of increase, scientists predict that the Edwards Aquifer will be so depleted that flow from the San Marcos Springs will cease around 2000 and flow from the Comal Springs will be severely reduced. Without the cooperation of state and local agencies to reduce the amount of groundwater extracted from the aquifer, recovery of the fountain darter is considered unlikely.
Conservation and Recovery
In 1993, the U.S. Fish and Wildlife Service (FWS) and several cooperators began studies in the Comal Springs ecosystem designed to study habitat use and to model instream flow requirements for the fountain darter and another potentially threatened species, the Comal Springs riffle beetle (Heterelmis comalensis ). Results of the studies were not yet available when the revised Recovery Plan was published in 1996, but were expected to provide additional population and density estimates for the two species. In 1994, the FWS and cooperators initiated a similar study in the San Marcos system.
The 1996 San Marcos/Comal (Revised) Recovery Plan, which covers the fountain darter and four other listed species of the Upper San Marcos, notes that recovery goals for the habitats' species include the survival of these species in their native ecosystems; the development of an ecosystem approach using strategies to address both local, site-specific, and broad regional issues related to recovery; and the conservation of the integrity and function of the aquifer and spring-fed ecosystems that these species inhabit.
Delisting is considered unattainable for all five species (including the fountain darter) due to the potential for extinction from catastrophic events, especially from reduced water flows as a result of drought. Consequently, the revised Recovery Plan calls for the establishment and continued maintenance of refugia capability for all five species in case of a catastrophic event. Though delisting is considered unlikely, downlisting is considered a possibility for the fountain darter, possibly as early as 2025 if continuous progress is made.
Schenck, J.R., and B.G. Whiteside. 1976. "Distribution, Habitat Preference and Population Size Estimate of Etheostoma fonticola." Copeia 1976:697-703.
U.S. Fish and Wildlife Service. 1980. "Determination of the Fountain Darter (Etheostoma fonticola) as Endangered." Federal Register 45:47355-47364.
U.S. Fish and Wildlife Service. 1984. "San Marcos River Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.
U.S. Fish and Wildlife Service. 1996. "San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.
"Fountain Darter." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (January 22, 2019). https://www.encyclopedia.com/environment/science-magazines/fountain-darter
"Fountain Darter." Beacham's Guide to the Endangered Species of North America. . Retrieved January 22, 2019 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/fountain-darter