Micropterus coosae

Geographic Range

Redeye bass ( Micropterus coosae ) are Nearctic freshwater fish native to the Coosa River Basin, encompassing eastern Alabama, northwestern Georgia, Polk and Bradley counties in Tennessee, and western South Carolina. The Coosa River, the Alabama River, and the Tallapoosa River all meet up to form the ACT River Basin. These fish can also be found in the Savannah River in South Carolina and Georgia but primarily inhabit smaller shallow streams throughout all these systems. Redeye bass were introduced to the Stanislaus River, the Feather River, Alder Creek, and Santa Margarita River on the west coast of California. On the east coast, redeye bass were introduced to Kentucky in parts of the Cumberland River, specifically in Martin’s Fork in Harlan County. In the Neotropical region, redeye bass have been introduced to some rivers and streams in Puerto Rico.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
  • native native
• neotropical neotropical
  • introduced introduced

Habitat

Redeye bass are freshwater bass that live in small creeks, rivers, and waterfalls in the temperate zones. Redeye bass have also been introduced into some reservoirs and lakes such as Lake Keowee. These bass are commonly found in relatively shallow water, typically at depths of ca. 0.5 to 0.6 m, and Knight (2011) reported ideal current velocities of 0.13 m/s. They also choose shoreline areas rather than mid-stream habitats, likely for the cover opportunities from undercut banks and downed logs along the edge. This environment allows the fish to avoid predators while staying close to the surface where they feed.

Larger redeye bass can be found in deeper, warmer water sections, mainly when there are instream features that provide cover. They are associated with microhabitats with a greater proportion of boulders. Juvenile bass live in deeper portions of the water, reaching depths of up to 3 m. Juveniles also choose microhabitats with more canopy cover and pools with slower current velocities.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

Physical Description

Redeye bass are smaller fish among the members of the genus Micropterus , usually weighing 170 g to 450 g; the largest individuals can weigh up to 2300 g. Adult redeye bass typically reach lengths of 15 to 47 cm. Sexual dimorphism is present in this species, as females are slightly larger than males. Redeye bass eyes are bright red (hence, the common name).

Internally, these fish have 31 to 33 vertebrae. They possess sharp pointed teeth that are used for grabbing and holding prey. Redeye bass have brown to green colored scales and black stripes that run laterally along the fish. Redeye bass also have a dorsal fin, an anal fin, a caudal fin, two pelvic fins, and two pectoral fins. These fish are ectothermic, which means they rely on external sources such as the sun to regulate their body temperatures.

Redeye bass hatchlings are 2.2-2.5 cm in length and weigh 0.1 g. As juveniles, these fish reach a little over 5 cm in one year and grow another 2.5 cm every year until the ages of 6 to 8, at which point the growing process would slow. These fish, as juveniles, have less coloration on their lateral striped scales but still have the same green coloration. These fish also still have red eyes, but it less noticeable than in mature bass.

Redeye bass differ from others in their genus by the presence of their red eyes. The eyes may have slight tints of white on the posterior parts of the eyeball. Redeye bass may also lack vertical bars just beyond their operculum, with congenerics may possess the bars. The pattern of spots on the midline varies among species, as well. Finally, redeye bass have red edging along their dorsal, pectoral, and tail fin, when other species have yellow, orange, or green colors.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Redeye bass eggs have not been described, but it is known that females lay 2,000 to 3,000 eggs at a time in a gravel nest made by the males. Egg sizes for redeye bass are 3.5 mm. Once the eggs are fertilized, it takes 1-10 days for the eggs to hatch. As fry, redeye bass are 22-25 mm in length and weigh 0.1 g. In their first year, these bass grow 5 cm, then 2.5 cm every year thereafter. Redeye bass experience indeterminate growth, which means they never stop growing. Near the end of life for redeye bass, growth tends to slow to an undetermined number, but not 2.5 cm every year.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Redeye bass are polygynandrous fish that search for a new mate every spawning season. Redeye bass breeding habits are similar to smallmouth bass ( Micropterus dolomieu ) in many breeding respects including courting. Male bass will often bump and circle the potential mates. Male redeye bass will build nests in gravel patches or loose branches in shallow water a couple of weeks before they start the breeding process. Spawning begins when water temperatures reach 17 to 21 °C. Female redeye bass lay their eggs in the nests and the male redeye bass externally fertilize the eggs in the nest.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Redeye bass are oviparous, seasonal breeders, mating from late May to early July. Like most fish, redeye bass are iteroparous, which means they will spawn in this time frame almost every year. They reproduce sexually, using external fertilization. Females usually lay between 2000 and 3000 eggs at a time, though they can spawn multiple times a year if the water conditions remain favorable. These eggs will be externally fertilized by males that will then protect the eggs from predators. Usually, these eggs will take 1-10 days to hatch with a common range being between 5-7 days. Hatch time varies depending on water temperature, with warmer temperatures leading to faster hatching times. Redeye bass fry are about 22-25 mm long and weigh about 0.1g. They leave their nest shortly after hatching to live in groups with other recently hatched redeye bass.

Female redeye bass reach sexual maturity at two to three years of age, and males reach sexual maturity slightly earlier, at two years of age. Knight (2011) reported that redeye bass in his study mostly reached maturity at age 2, with a few reaching it at age 1 and others not being active at age 3. He noted that body length was the strongest predictor of maturity. However, he speculated that the young-but-mature fish contributed fewer eggs than larger, gravid females.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Male redeye bass start the mating process by building the nest to house the eggs. Once the eggs are laid, the males stay and protect them from predators, and fan the eggs with their tails to keep them oxygenated. Once hatched, the hatchlings are independent. Females provide no parental care beyond the act of mating.

• Parental Investment
• no parental involvement
• pre-hatching/birth
  • provisioning
    • male

Lifespan/Longevity

Redeye bass are suspected to have a maximum age of 10 years, based on the oldest captures in the wild. Expected age has not been reported in the literature. Because redeye bass are not often held in captivity, longevity has not been reported.

Eggs and fry may be subject to predation from other larger redeye bass. As adults, habitat loss affects longevity.

Behavior

Redeye bass communicate audibly and visually. Redeye bass use acoustic signals such as low-frequency pulses when communicating audibly. When redeye bass communicate visually and tactilely, they often use physical contact and circling other fish. These behaviors are used for reproduction and survival. When redeye bass sense danger, they use a variety of these methods to communicate incoming threats, such as the pulses or circling fish.

Redeye bass courting starts when a male redeye bass find female redeye bass and will begin bumping them and circling them, showing mating readiness. Male redeye bass make nests before looking for female partners, and these nests are usually in gravel or near protection to hide from predators. Redeye bass migrate to more open and larger channels during the winter months and migrate towards streams and shallower water during the spring and summer months. Once the nest is made, female redeye bass drop their eggs, and the males externally fertilize them and protect them until they hatch.

After they hatch, hatchlings will live in social groups to help stay protected from predators until they reach adulthood. Redeye bass are motile and natatorial fish, so they rely heavily on swimming when feeding. They are also diurnal..

These fish mainly eat terrestrial insects, salamanders, crayfish, and larval insects. Most of their feeding comes from swimming to the surface and feeding. For many redeye bass, males will go extended periods of time without eating when protecting their nests, which will lead to them eating newly-hatched fry.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• social social

Home Range

Redeye bass display variety in their home range, specifically regarding size and age. Larger, older redeye bass usually have smaller home ranges, while smaller, younger redeye bass usually have larger home ranges. A 10-week study by Knight (2011) recorded that the average linear movement of adults was 705m. While these fish have not had their nest sizes reported, it is suspected that they increase with size, so bigger redeye bass have bigger nests. During the breeding season, the males’ territory consists of the size of the nest. Females do not defend a territory.

Communication and Perception

Redeye bass are relatively aggressive fish and will often compete for space using a variety of visual and tactile gestures, including nudging, jerking, and circular motions in their swimming. These fish also communicate using acoustic noises, such as low-frequency pulses, and have up to 41 tones. Redeye bass also use their internal ears to perceive their surroundings. These bass often make acoustic noises to each other for communication, but sometimes to warn of danger and other threats. Another way that fish can communicate is through chemical and tactile cues. Fish often use pheromones and physical contact to communicate, whether for reproduction purposes or species identification.

Redeye bass use their eyes in light and dim environs. These fish are mainly diurnal, but can make smaller movements at night. The protruding eyes on the lateral parts of their heads allow for good peripheral vision, but in return, reduces their bilateral vision. While these fish mainly use their eyesight for hunting, they also rely heavily on their sense of smell, including chemicals and pheromones, to detect changes in their environment. Another way that bass sense their surroundings is through lateral lines. Redeye bass use these lateral lines to detect vibrations, pressure, and movement of water.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Redeye bass are carnivorous, shallow-water fish and are insectivores and piscivores. Part of these fish diets are land creatures that are close to the water, such as terrestrial insects and salamanders. These fish also feed on crayfish, larval aquatic insects, and other smaller fish.

In their non-native environment in California, they feed on red swamp crayfish ( Procambarus clarkii ) and large insects. As juveniles, redeye bass in their non-native environment eat mainly smaller insects, consuming larger insects as the fish grow. By the time they are adults, crayfish make up 90% of their diet by weight. The remaining 10% of the diet was comprised of aquatic insects, like dobsonflies (Neuroptera), mayflies (Ephemeroptera) and damselflies (Zygoptera). The largest redeyes consumed two fish species: a Pacific lamprey Entosphenus tridentatus and a prickly sculpin Cottus asper .

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • piscivore piscivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• amphibians
• fish
• insects
• aquatic or marine worms
• aquatic crustaceans

Predation

The two main predators of redeye bass are humans ( Homo sapiens ) and larger redeye bass. Humans mainly fish for them as sport rather than for a food source due to their size. The main predator of young redeye bass is larger redeye bass, because male redeye bass will opportunistically eat hatchlings. Some other black bass species are preyed on by large birds, but there is no research to support this for redeye bass. An adaptation that redeye bass use to protect themselves against predators is their cryptic scale color, which allows them to go undetected. Redeye bass have a green and brown coloration that blends in with their habitat.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Redeye bass in their native environment are the top predators but they do have some predators outside their environment, such as large birds and humans ( Homo sapiens ). They feed on crayfish, larval insects, terrestrial insects, salamanders, and juvenile redeye bass.

Redeye bass are at risk of parasites, including amoebas ( Acanthamoeba polyphagia ), monogeneans ( Cleidodiscus banghami ), nematodes ( Uvulifer ambloplitis ), and trematodes ( Leptocleidus ).

Economic Importance for Humans: Positive

Redeye bass are a form of ecotourism for many of the states where they live. These fish are a very desirable catch by many anglers and are fished for sport, especially in Alabama.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

Redeye bass were introduced into California river systems and are considered invasive. Their invasion is harming native fish in California and slowing down conservation efforts in the area. This hit to conservation corresponds to financial strains for humans.

Conservation Status

Redeye bass are a species of “Least Concern” according to the IUCN Red List. They have no special status on Michigan Natural Features Inventory, the CITES appendices, and the USFWS Endangered Species database.

Threats are minimal but include redeye bass hybridizing with Alabama spotted bass ( Micropterus punctulatus ) in Lake Keowee (South Carolina), where both bass species were introduced. There are no other major threats within their natural range.

Because redeye bass have a stable population in their native environment, no conservation efforts are in place. Creel limits in their native ranges may help with sustainability, such as 10-a-day limit in Alabama and 5-a-day limit in North Carolina. In their non-native environment, such as California, there are no current large-scale projects to remove these bass.

Additional Links

Encyclopedia of Life

Contributors

Andrew Burchette (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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