About Etheostoma swaini (Jordan, 1884)
Etheostoma swaini, commonly known as the gulf darter, is a species of freshwater ray-finned darter. It belongs to the subfamily Etheostomatinae, which is part of the Percidae family that also includes perches, ruffes, and pikeperches. This species is found in the U.S. states of Louisiana, Mississippi, Alabama, Florida, Tennessee, and Kentucky. It is a colorful fish; mature males have vertical red-orange and blue-green barring near the tail, and the species grows to a maximum length of around 7.8 centimeters (3.1 in). The gulf darter is typically found in small to medium-sized creeks, very often in extremely shallow water. It lives over sandy bottoms and among aquatic vegetation, particularly Sparganium americanum, and forages for insect larvae and small invertebrates among plants and organic debris. The International Union for Conservation of Nature has assessed this species' conservation status as least concern. The gulf darter generally inhabits small to moderate-sized creeks, occurring over sand or sandy mud bottoms, and is often found near aquatic vegetation or a layer of organic debris. Its range extends from Lake Pontchartrain, Louisiana east to the Ochlockonee River drainage in Florida, and also includes many eastern tributaries of the Mississippi River from Buffalo Bayou, Mississippi, north to the Obion River system in Tennessee and Kentucky. It is frequently encountered in extremely shallow locations, often foraging in water less than 5 centimeters (2.0 in) deep. In most creeks, the gulf darter's microhabitat has moderate to heavy amounts of aquatic vegetation, primarily Sparganium americanum. These fish actively forage in and among vegetation clumps, and use areas of reduced current downstream of these clumps as resting spots. In larger, heavily vegetated creeks, it occupies quiet streamside areas with sand or sand-silt substrates. In the smallest creeks, however, the gulf darter may occasionally be found in shallow, swift riffles formed by logs, rocks, or vegetation. This species has a low tolerance for brackish water. In its preferred microhabitat, the gulf darter is usually found alongside the speckled madtom (Noturus leptacanthus) and the blackbanded darter (Percina nigrofasciata), and often shares habitat with larvae of the southern brook lamprey (Ichthyomyzon gagei). The blackbanded darter is the species most ecologically similar to the gulf darter, but the extent of any potential competition between the two is unknown. The blackbanded darter forages across a much wider variety of microhabitats, and does not use vegetation or organic debris as extensively as the gulf darter. The gulf darter is classified as an insectivore, feeding on small invertebrates including black flies, mayflies, and dragonflies. One study found that larval dipterans are the most important food source for gulf darters of all sizes, with chironomids found in 71–100% of all examined fish stomachs. The primary predators of the gulf darter are likely larger freshwater fish, including burbots (Lota lota), stonecats (Noturus flavus), and smallmouth bass (Micropterus dolomieu). Like many other darter species, gulf darters can maintain their position on the substrate in flowing water. This unique trait plays a key role in shaping the species' microhabitat preferences.
