The redeye bass, redeye, or Coosa bass (Micropterus coosae) is a species of freshwater fish in the sunfish family (Centrarchidae).The small bass is endemic to the Mobile and Alabama River systems, more specifically the Coosa River, which is a major tributary to the Alabama River in Georgia and Tennessee.
Systematics
Taxonomy and classification
Redeye historically have been under-described compared to other centrarchids (sunfish). The osteology (skeleton) of M. coosae fits the general centrarchid (sunfish) pattern. These similarities in anatomy provide a gateway into understanding evolutionary relationships for future taxonomic and phylogenetic research. Etymologically, the redeye bass was named by American Ichthyologists Carl Hubbs and Reeve Bailey in 1940 upon discovery of the holotype (first official specimen). The species name “coosae” derives from the Coosa River system in Georgia, its native region. Prior to Hubbs's and Bailey's later research, M. coosae was taxonomically considered to be a small form of smallmouth bass. This misconception may be due to redeye bass's tendency to hybridize with smallmouth and spotted bass, as seen in California.
Similar and co-occurring species
Two native species of fish have the most prominent similarity to redeye bass in terms of diet and habitat – the Rainbow Trout (Oncorhynchus mykiss), and Sacramento Pikeminnow (Ptychocheilus grandis). These fishes can co-occur with redeye bass in small numbers below refuge areas. Additionally, redeye bass are often confused with the recently (1999) described shoal bass (M. cataractae) from Alabama, Georgia, and Florida, which is sympatric (occupying the same geographic area) with redeye bass. Before the formal description of shoal bass by James Williams and George H. Burgess in 1999, shoal bass were often considered a type of redeye bass and were sometimes called the "Flint River form of Redeye Bass". In 2013, the redeye bass showed additional species-level variation: Micropterus cahabae, restricted to the Cahaba River system; Micropterus tallapoosae, restricted to the Tallapoosa River system; Micropterus warriorensis, from the Black Warrior River system; and Micropterus chattahoochae, from the Chattahoochee River system. Naturally, Micropterus coosae resides in the Coosa River system. The redeye bass's most recent common ancestor (MRCA) can be dated to approximately 7.39 million years ago (Mya), with a potential range between 4.63 and ten Mya. The most recent speciation events from the largemouth and spotted bass likely happened between 0.68 and 0.76 Mya.
Description
Body color and pattern
thumb|M. coosae held using "lipping" technique|left
Redeye bass are distinguished from other species of black basses due to a couple of subtle, but diagnostic features; the presence of a distinct silver-white crescent on the posterior (back) one-half of the eyeball, iridescent white, turquoise, or red on upper and lower margins of the caudal fin, a shallow emargination (notch) between the dorsal fins, and the absence of a dark mid-lateral (side) stripe along the body. Unique from all other black basses, redeye typically have three dark bars on the cheek. Most individuals (about 76%) have 0–6 vertical black blotches near the front of the body, followed by softer spots toward the back. The back and sides of the fish are generally olive to brown with darker brown mottling.
Fin shape and features
The anterior (front) dorsal fin has dark green spines tipped in white with translucent green membranes, while the posterior (back) dorsal fin is red with the front five or six rays tipped in white; the base is green, the upper half red, and the last few membranes are transparent. The caudal fin is green at the base and red at the tips, with translucent membranes and a thin white border on the top and bottom edges. The anal fin is dark green at the base, red toward the tip, and edged in white, with membranes shifting from greenish white at the base to red in the middle and clear near the edge. The pelvic fins are white with black streaks, and the membranes are translucent white, while the pectoral fins have red rays with transparent membranes. Many redeye bass world record listings, especially those over are actually records for the shoal bass.
thumb|200px|left|[[Fly rod-caught redeye bass, Tallapoosa River, Tallassee, Alabama (Released)]]
The rock bass (Ambloplites rupestris), a distinct species of Centrarchid, is sometimes called the redeye or redeye bass in Canada.
Species distribution
The redeye bass is a predatory fish that is endemic to the Coosa River system in the southeastern United States, including Georgia and Alabama.
thumb|650x650px|Reported global distribution of Micropterus coosae (U.S. Fish and Wildlife Service)
As an introduced species
In 1962 and 1964, redeye bass were introduced in California to provide angling (hook on a line to catch fish) in streams dominated by native fishes not favored by anglers, examples being introductions into the Stanislaus River (Tuolumne County), Feather River (Butte County), Alder Creek (Sacramento County), and Santa Margarita River (San Diego County). within the Santa Maria River basin. Introduced Micropterus coosae have displaced native hardhead (Mylopharodon conocephalus) in the Cosumnes River.
Coosa bass were also introduced into the Verde River and it's tributaries, of North Central Arizona. The introduction of these fishes were mistakenly imported to the region from Alabama thought to be smallmouth bass, and have since become well established since their introduction during the mid-1950s; in around 2021 these fishes were genetically identified as Micropterus coosae. Elsewhere, the redeye bass was introduced to Tennessee in the 1950s and has hybridized extensively with native smallmouth bass (M. dolomieu).