Etheostoma blennioides

Geographic Range

Etheostoma blennioides , the greenside darter, is restricted to a few major watersheds of North America. Its range extends from New York and the Potomac River drainage west to Kansas and south to Oklahoma, Arkansas, Mississippi and Alabama, mostly within the Mississippi River and its tributaries. Etheostoma blennioides is also found in the Lake St. Clair and Thames River system in Southwestern Ontario, Canada. Greenside darters are most common in creeks and rivers in east-central North America. However they are considered to be of "special concern" in Kansas and Mississippi and rare in Canada (Dalton, 1991).

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Greenside darters are benthic organisms and spend their lives associated with the substrate. They live in deep riffle habitats consisting of cobble and loose boulders covered by filamentous green algae, upon which they lay their eggs (Bunt et al., 1998). These fish also prefer moderate to fast-moving water of low turbidity (Dalton, 1991).

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• benthic benthic
• lakes and ponds
• rivers and streams

Physical Description

Etheostoma blennioides are small members of the perch family, first discovered by naturalist Constantine Rafenesque in 1819 (Dalton, 1991). Like all darters, greensides lack a swim bladder and live on the bottom substrate (Jenkins and Burkhead, 1993). They average 76 mm in total length, with a cylindrical body (Dalton, 1991) covered with ctenoid scales (Scott and Grossman, 1998) and a broad, triangular head (Dalton, 1991). Their eyes are large and located on each side of the apex (Discover Life in America, 2004). The snout is bluntly rounded, with a small terminal mouth (Dalton, 1991). They have two separate but closely-spaced dorsal fins (Dalton, 1991); the first dorsal fin is edged in white and has 12-14 hard spines, while the second has streaks of black and contains 13-16 soft rays and extends above the first fin (Jenkins and Burkhead, 1993; Bailey et al., 2004). There is also a small sharp spine on the posterior of the opercle. The pectoral fins are large and well-developed, the pelvic fins are located anteriorly, and the caudal fin is often slightly indented (Jenkins and Burkhead, 1993). The caudal, anal, and pelvic fins are all light green in color (Dalton, 1991).

The dorsal surface is olive-green or brown with dark red spots on the upper sides and at the base of the dorsal fins (Dalton, 1991). There are also two dark lines on the face, one extending downward from the eye to the snout and one extending from the eye to the maxillary (Scott and Grossman, 1998). The dark lateral patterning lightens to pale green down the sides, and gradually fades into a white ventral surface. The lower lateral sides have a dark green pattern of five to seven V-shaped bars. These bars are especially dark and visible on juveniles, who also have more pointed pelvic fins than adults (Scott and Grossman, 1998). Males are generally larger overall and also have larger anal, pectoral, pelvic, and first dorsal fins than females (Miller, 1986). Coloration also differs between sexes during the breeding season; males develop intense green to blue-green coloration on the lower sides, anal fins, pelvic fins, and head. The spiny dorsal fin, soft dorsal fin, caudal fins, and lower portions of the pectoral fins in male greenside darters may also become bright green, while the V-shaped lateral pattern turns into green vertical bars (Discover Life In America, 2004 ).

There are 4 different subspecies of Etheostoma blennioides : Etheostoma blennioides blennioides , E. b. newmanii , E. b. gutselli , and E. b. pholidotum . The best way to tell them apart is through scale counts and number of dorsal rays. E. b. newmanii has the highest scale count, the most dorsal rays, a fully scaled belly, and a well-developed upper lip. E. b. blennioides has fewer scales and dorsal rays than pholidotum. They also have more lateral blothes and a naked (scaleless) belly. E. b. gutselli has low scale counts, an anteriorally naked belly, no upper lip tip, and lack opercle scales. E. b. pholidotum has lower scale counts than E. b. newmanii and E. b. blennioides , as well as a small lip tip, and a completely scaled belly. E. b. newmanii and E. b. gutselli are considered to be more primitive forms of darter (Miller, 1968).

Greenside darters can be distinguished from other darters by their larger size, rounded snout, and coloration pattern: the rainbow darter ( Etheostoma caeruleum ) is bright blue and orange and has a pointy snout, while the johnny darter ( Etheostoma nigricans ) is brown and tan (Bailey et al., 2004).

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

• Sexual Dimorphism
• male larger
• male more colorful

Development

At fertilization eggs are laid on algae, close to the point of attachment with a rock. Afterwards, no more parental protection is given. The eggs will hatch 18-20 days after fertilization in water between 13 and 15 degrees celsius. The fry are pelagic, totally transparent (Muller, 2000), and live off their yolk sacs for the first six days after hatching (Dalton, 1991). Greenside darters are very delicate when they first hatch, and even very small changes in feeding or water quality can cause mortality (Muller, 2000). They begin feeding on plankton eight days after hatching (Dalton, 1991). After approximately two weeks, the fry start going to the bottom and acting like adults. Initial growth is rapid; fry attain lengths of about 50-55 mm by age 1 (Discover Life In America, 2004), at which time they also reach sexual maturity. Etheostoma blennioides is short lived, typically surviving for three years, though some live up to 4 or 5 years (Dalton, 1991).

Reproduction

Both sexes of greenside darters reach sexual maturity and spawn in the spring 1 year after hatching. Breeding only occurs when the water temperature has reached and remained at at least at 10.6 degrees Celsius for several days. Spawning is also restricted to riffle habitats containing boulders and rubble covered in filamentous algae. Greenside darters spawn in pairs, although both sexes are promiscuous and will spawn with many different partners over the course of one breeding season. It takes 10-12 bouts of spawning over a 4-5 week period for each female to deposit all her eggs. Males perform an elaborate ritual to establish dominance and claim territory, although the female will choose the actual spawning site (Dalton, 1991).

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

The breeding season of Estheostma blennioides is from April to June; spawning activity peaks in May. Spawning will not occur until the water temperature warms to at least 10.6 degrees Celsius. Greenside darters prefer to spawn in riffle areas with large amounts of filamentous algae. However, they have been observed to spawn over substrate alone. Males select a small area (100 cm in diameter or less) to defend as their mating territory, and then proceed to initiate spawning through elaborate courtship dances (Radabaugh, 1989). The pair may also chase each other around prior to spawning (Muller, 2000). Once a pair is formed, the female selects a site in algae and takes up an angled postion. The male will then mount and the two fish vibrate in unison for several seconds while the eggs are released and fertilized (Miller, 1968). Eggs are typically laid in batches of anywhere from 2 to 192 (Smith, 1985). These fertilized eggs are demersal and adhesive; the female lays them on the algae right above where it attaches to the rock, where they remain until hatching (Dalton, 1991). Males will sometimes remain in the area to guard the eggs until hatching (Smith, 1985). A pair may spawn more than once at short time intervals (Miller, 1968). Both sexes will also spawn with many different partners over the breeding season (Dalton, 1991).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Most darters provide little or no parental care other than attaching their fertilized eggs to the bases of filamentous algae where they are less visible to predators (Dalton, 1991). The only additional parental investment observed in E. blennioides is the guarding of fertilized eggs by the male parent (Radabaugh, 1989). This may become more difficult over the course of the spawning season as these males continue to mate with multiple females.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • protecting
    • male

Lifespan/Longevity

Etheostoma blennioides typically lives up to 3 or 4 years in the wild. Lack of both food and habitat can potentially limit growth and survival (Bunt et al., 1998). For example, spawning will often only occur in riffle areas with filamentous algae beds. Darters such as E. blennioides are also extremely sensitive to siltation and turbidity. Excessive sediment smothers eggs, and decreases the abundance of certain common prey items, such as Ephemeroptera (Shiels, 2003), and may also affect darter reproduction by blocking light needed for filamentous algae to grow in darter spawning habitats (Dalton, 1991).

Behavior

Greenside darters lack a swimbladder and are therefore a benthic-dwelling organism. Fairly reclusive, they spend much of their time hovering directly above the substrate or hiding in overhanging rock caves (Katula, 2000). As the name suggests, darters have a unique ability to maneuver quickly within and around large substrate as they forage along the bottom (Shiels, 2003). This movement is accomplished by assuming a "snake-like position" in which the pelvic and caudal fins, as well as the caudal peduncle, are rested on a rock while the head is raised and the tail held at angle to the body. Sweeping actions of the pectoral fins allow the fish to move along the substrate while the caudal serves as a holdfast. The fish rotate sideways to recede under rocks, again using the caudal fin as an anchor. To travel longer distances of several meters, they will put on a burst of speed (i.e. dart) using the caudal fin (Dalton, 1991).

Greenside darters are daytime predators who rely on visual stimuli (Wynes and Wissing, 1982) to locate their benthic invertebrate prey among the rocks, gravel or sand along the stream bottom (Shiels, 2003). They in turn depend heavily on their cryptic coloration to avoid other fish predators (Radabaugh, 1989). Although they do not have a hierarchical social structure, male E. blennioides will claim and defend small territories during the spawning season (Radabaugh, 1989).

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• territorial territorial

Home Range

Greenside darters inhabit riffle runs with cobble or boulder substrate in streams and rivers on the eastern side of North America (Dalton, 1991). During the spawning season, each male will select and defend a small area 100 centimenters in diameter or less (Radabaugh, 1989).

Communication and Perception

Like many other percids, darters communicate mainly through coloration. Males use their bright body coloration to display agression to other males and to court females. Similarly, females may signal to males through changes in body color contrast (McFarland and Strange, 2003).

• Communication Channels
• visual visual

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

Food Habits

In general, greenside darters feed on immature benthic insects in the 1-6 mm range (Wynes and Wissing, 1982), although this diet varies with season and prey availability (Gray et al., 1997). Chironomid larvae (midges/flies) are the major prey taxon consumed, Ephemeroptera (mayflies) and Plecoptera (stoneflies) larvae are also common prey items (Hlohowskyj and White, 1983). Ephemeroptera and Simuloidii (blackflys) are a larger portion of the diet during the winter (Hlohowskyj and White, 1983). Prey size and taxa consumed also shifts from juvenile to adult; juveniles consume smaller prey and more chironomids than adults. Females also tend to consume more than males, expecially during the spawning season (Gray et al., 1997).

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects

Predation

There has been a lack of research on fish predators of E. blennioides , although both smallmouth bass and several kinds of trout ( brook , brown , and rainbow ) have been observed to prey on darters. A more common predator is the avian common merganser , which often stops and feeds in darter habitats during its northward spring migration (Englert and Seghers, 1983).

Many darters avoid predation by other fish through a behavior known as "freezing" -- when a predator is present, the fish will simply stop moving for a specified amount of time, and then resumes normal activity levels again. This avoidance tactic is linked to coloration. Freezing is the best strategy for non-breeding males, whose cryptic coloration helps camoflauge them against the stream bottom. However, in the breeding season, brightly colored male darters may try to flee instead of freeze. However, for E. blennioides , the bright green breeding color is actually further protection, as it blends in well with filamentous algae habitats preferred for spawning (Miller, 1968).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Besides serving as both predators and prey in their ecosystems, E. blennioides also plays an integral role in the reproductive cycle of several freshwater mussels, including endangered species(Upper Thames River Conservation Authority,2003). Microscopic mussel larvae, also known as glochidia, attach to the gills of certain fish, including E. blenniodes , immediately after they are released into the water. Because mussels cannot swim, the fish provides their means of transport and distribution into other areas of the stream. As a result, the continued existence of these mussels is directly linked to that of its greenside darter hosts (Shiels, 2003).

Economic Importance for Humans: Positive

While E. blennioides has no commerical value and are not regarded as a sport fish, they are often used as aquarium species (Dalton, 1991). They are also useful for scientific investigations of food resource partitioning and habitat selectivity because they share many characteristics with other members of their genus (i.e. Etheostoma caerulum , E. nigrum , E. flabellare ) and can be easily compared (Hlohowskyj and White, 1983).

• Positive Impacts
• pet trade pet trade
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of E. blennioides on humans.

Conservation Status

Although greenside darters are not officially listed as endangered or threatened, they are considered vulnerable in Canada and rare in Kansas and Mississippi (Dalton, 1991).

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Sharon Graham (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor, Renee Sherman Mulcrone (editor).

References

Bailey, R., W. Latta, G. Smith. 2004. An Atlas of Michigan Fishes . Ann Arbor, MI: Miscellaneous PUblications, Museum of Zoology University of Michigan.

Bunt, C., S. Cooke, R. McKinley. 1998. Creation and maintenance of habitat downstram from a weir for the greenside darter, Etheostoma blennioides -- a rare fish in Canada. Environmental Biology of Fishes , 51 (3): 297-308.

Dalton, K. 1991. Status of the Greenside Darter, Etheostoma blennioides , in Canada. Canadian Field-Naturalist , 105 (2): 173-178.

Englert, J., B. Seghers. 1983. Predation by fish and common mersangers on darters (Pisces: Percidae) in the Thames River Watershed of southwestern Ontario. Canadian Field Naturalist , 97 (2): 218-219.

Gray, E., J. Boltz, K. Kellogg, J. Stauffer. 1997. Food Resource Partitioning by NIne Sympatric Darter Species. Transactions of the American Fisheries Society , 126 (5): 822-840.

Hlohowskyj, I., A. White. 1983. Food Resource Partitioning and Selectivity by the Greenside, Rainbow, and Fantail Darters (Pisces: Percidae). Ohio Journal of Science , 83 (4): 201-208.

Jenkins, R., N. Burkhead. 1993. Freshwater Fishes of Virginia . Bethesda, Maryland: American Fisheries Society.

Katula, R. 2000. "Tropical Fish Hobbyist" (On-line). The Captive Maintenance of Darters. Accessed October 28, 2004 at http://www.nativefish.org/Articles/Darter_Diet.htm .

McFarland, K., R. Strange. 2003. "Percis III: The Third International Percid Fish Syposium" (On-line). Evolution of Color and Contrast Communication of Darters. Accessed October 28, 2004 at http://cstl-csm.semo.edu/rstrange/research/meetings.htm .

Miller, R. 1968. A Systematic Study of the Greenside Darter, Etheostoma blennioides Rafinesque (Pisces: Percidae). Copeia , 1: 1-40.

Muller, B. 2000. Spawning and Raising the Greenside Darter, Etheostoma blennioides , with a Note on the Eggs of the Rainbow Darter, E. caeruleum . American Currents , 26 (2): 11-12.

Radabaugh, D. 1989. Seasonal Color Changes and Shifting Antipredator Tactics in Darters. Journal of Fish Biology , 34: 679-685.

Scott, , Grossman. 1998. Freshwater Fishes of Canada . Ontario, Canada: Galt House Publishing.

Shiels, A. 2003. "Pennsylvania Fish and Boat Commission" (On-line). Pennsylvania's Dynamic Darters. Accessed October 28, 2004 at http://sites.state.pa.us/PA_Exec/Fish_Boat/education/catalog/darters.html .

Smith, C. 1985. The Inland Fishes of New York State . New York, NY: New York State Department of Environmental Co..

Wynes, D., T. Wissing. 1982. Resource Sharing Among Darters in an Ohio Stream. American Midland Naturalist , 107 (2): 294-304.

2004. "Discover Life in America" (On-line). Greenside darter. Accessed October 25, 2004 at http://www.dlia.org/atbi/species/animals/vertebrates/fish/Percidae/E_blennioides.html .

2003. "Upper Thames River Conservation Authority" (On-line). More on Freshwater Mussels. Accessed October 28, 2004 at http://www.thamesriver.org/Species_at_Risk/more_about_mussels.htm .