Little is known of communication between members of this species. They are able to perceive their environment using vision, hearing, chemoreception and can sense vibrations with the lateral line system.
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
Specific predators of emerald darters are not known. Their defenses against predators include cryptic coloration. Bright dorsal colors may help darters in riffles with multicolored rocks to be concealed, and darters with green coloration may be found living in algae (a habitat noted previously for this species, although not a primary one). In addition, horizontal bars in riffle darters may serve to interrupt the outline of the fish to confuse predators.
Anti-predator Adaptations: cryptic
Etheostoma baileyi is a member of the snubnose darter subgenus (Ulocentra), and shares several characters with others in the group, including a blunt snout, small mouth, broadly joined gill membranes, five branchiostegal rays, scales on the belly, a humped nape, and 8 to 9 dorsal saddles with a roughly square appearance. Other snubnose darters include E. zonale, E. coosae, E. simoterum, E. barrenense, E. rafinesquei, E. etnieri, E. duryi, and E. atripinne. Of these, E. baileyi shares a present but narrow premaxillary frenum and lack of vomerine teeth with E. simoterum, E. barrenense and E. rafinesquei.
Emerald darters are moderately sized darters (standard length 27.8 to 49.9 mm; body depth 15.9 to 21.1 mm), although they are one of the most delicate bodied species within their subgenus. Males tend to be longer and have less body depth than females of similar age.
Etheostoma baileyi possesses a small, subterminal mouth, scaleless breast, and scaled cheeks, opercle and posterior nape. It has nearly colorless pectoral and pelvic fins with olive-dominant upper sides and white or yellowish ventral surface and lower sides. It has a complete lateral line composed of 44 to 56 scales. Gill rakers number between 8 and 10.
Emerald darters possess two distinct dorsal fins, the anterior containing spines only, and the posterior containing only soft rays. Clayton (1984) and Kuehne and Barbour (1983) differ slightly in published fin ray counts for the emerald darter. Clayton found a majority of individuals with 10 to 12 dorsal spines (rarely 13), while Kuehne and Barbour found 10 to 11 common, with 9 to 12 possible. Regarding dorsal ray count, Clayton’s specimens varied commonly from 10 to 12 with occasional individuals with 13. Kuehne and Barbour found 10 to 11 common, with a range of 9 to 12 possible. Both sources agree that pectoral fin rays are about 14, with Clayton specifying a range of 13 to 15. Both sources also agree on an anal fin ray count of 6 to 8. Clayton’s dissections of the species revealed a range of 38 to 41 vertebrae, which was previously unknown.
Coloration in emerald darters is sexually dimorphic, with females possessing a muted yellow or green body with a reddish brown upper margin on their spiny dorsal fin, and males exhibiting more various and saturated color, particularly from mid-winter through May. Males have green accents on their cheeks, opercles, anal fin, pelvic fin, basal portions of both dorsal fins and at the top and bottom of the caudal fin nearest the caudal peduncle. Breeding males boast a bright red band at the dorsal margin of the spiny dorsal fin, with highest saturation at the extreme anterior and posterior portions of the fin. Both males and females start to fade in color by the first week of June.
Males and females share similar general color patterns, including 8 to 12 lateral emerald green blotches and 7 to 10 dark green dorsal blotches (“saddles”). The lateral marks are evenly spaced and square with the exception of breeding males, in which the marks are extended into vertical bars. Dorsal saddles are fairly vague, especially closer to the caudal fin. The membrane of the spiny dorsal fin exhibits 2 to 3 light horizontal bands and the rays of the posterior dorsal fin possess 2 to 3 light bands. There is no regular pattern on the pigmented caudal fin. The fish possess a stippling of dark spots on the upper side. Three markings may surround the eye: a preorbital bar that does not extend continuously to the lip, a long but vague suborbital bar, and spots and a dark band behind the eye are sometimes present.
An additional difference in the sexes is observable in the genital papilla: males possess a short tube, whereas females’ papilla are longer and bent backward at the tip.
Banded darters (Etheostoma zonale) and Tennessee snubnose darters (Etheostoma simoterum) are similar in appearance to E. baileyi. Etheostoma zonale has fewer saddles (6) and lateral blotches that extend around the belly as bars, as well as a more pronounced snout. Although banded darters are close associates, being found in the same areas and similar microhabitat, they are able to tolerate swifter currents than E. baileyi, and the two are not known to hybridize in the wild. Tennessee snubnose darters have red spots on the upper portion of the body, and a spiny dorsal fin with irregular black lines and black marks along sides. Additional similar species include the more massive Etheostoma blennioides with only 6 to 7 dorsal saddles. Etheostoma simoterum atripinne, a species historically found in the Little South Fork of the Cumberland River, has more prevalence of red markings than E. baileyi, and 54 or more lateral line scales.
Range length: 27.8 to 49.9 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful
Many emerald darters have been captured that were aged up to three years. In the Red River drainage, 53% of the population survived into its second year, and 7.7 % into its third, with third year individuals being primarily male.
Typical lifespan
Status: wild: 3 (high) years.
Like most members of the family Percidae, emerald darters are adapted to a benthic existence. They can be found in a variety of clear freshwater lentic habitats with moderately low siltation and with several different substrates. Microhabitat selection is influenced by flood events, temperature and seasons. The fish typically are found in depths of 8 to 45 cm. However, they seek deeper rock-lined pools during winter months and when flooding alters current velocity and depth at riffles.
Streams in Kentucky known to have populations of emerald darters maintain temperatures of 0 to 25 degrees Celsius. When water temperatures are high, the fish can be found in riffles and runways with up to 0.61 m/s flow velocity.
Siltation is generally not well tolerated by this species. Because it ranges throughout the heavily strip-mined Cumberland Plateau, it is thought that coal siltation has likely reduced, but not eliminated, E. baileyi populations throughout its range.
Emerald darters prefer open areas with full sunlight over dense vegetation. However, areas with Potemogeton, Typha, Justicia, algae species and other submerged and emergent plants have produced collections.
Range depth: 0.08 to 0.45 m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: benthic ; rivers and streams
Emerald darters, Etheostoma baileyi, are found primarily in eastern Kentucky, with a small range extension into northeastern Tennessee. Their range is restricted to the Cumberland Plateau, including only the upper Kentucky and upper Cumberland River systems, specifically Red River, Jacks Creek, Buckhorn Creek, Redbird River and Indian Creek of the Kentucky drainage and Clear Creek, Station Camp Creek, Elk Creek and Poor Fork of the Cumberland River drainage, among others.
Interestingly, there are several sympatric darters below the falls of the Cumberland River, but E. baileyi is one of only a few darters also present above the falls. Etheostoma sagitta shares a similar limited range, and Kuehne and Barbour (1983) suggest that this is a result of a stream capture of the Cumberland River by the South Fork of the Kentucky River in recent time.
Biogeographic Regions: nearctic (Native )
Emerald darters are benthic feeders, as evident from their subterminal mouths. Prey items and amount of feeding is influenced by season and temperature. They feed primarily in the daytime, relying on vision to locate food items, as noted in related species. The major constituent of the diet, regardless of season, tends to be Chironomid larvae and pupae (family Chironomidae), with nemotodes and microcrustaceans also common, and the occasional caddisfly or mayfly larva.
Animal Foods: insects; aquatic or marine worms; aquatic crustaceans
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
Emerald darters are predators on aquatic insects, and are undoubtedly prey items as well, although their predators are not specifically known. Their parasites includes metacercarial tremetodes (Trematoda) which cause cysts, and leeches (Hirudinea). Additional ecosystem roles of emerald darters are largely unknown.
Commensal/Parasitic Species:
Emerald darters are important members of the ecosystems in which they live.
Emerald darters have no currently known negative effect on economics to humans.
Emerald darter larvae measure 4.5 to 6.4 mm in length when first hatched. Larvae emerge from the egg with yolk sacs. Temperature of water affects the speed of the hatch and the size of the emerging larvae, with warmer water resulting in a faster development, but smaller larvae. In laboratory hatching experiments, incubation time ranged from 172 to 384 hours with temperatures ranging from 17 to 21 degrees C. During the same experiments, Clayton (1984) noted that successful larvae exited the egg tail-first, and had relatively small yolk sacs. Initial spiraling motility of the larvae was replaced by a more darting movement after a few days.
The fish continue to grow throughout their lives, reaching an average total length of about 38 mm at one year, 45 mm at two years and 53 mm at three. Males tend to grow at a greater rate than females when young.
Emerald darters are threatened (although not currently state listed) in Tennessee due to limited range in the state and the threat of negative impacts on stream health due to strip mining for coal. The species is fairly common throughout its range in Kentucky.
US Federal List: no special status
CITES: no special status
Etheostoma baileyi was named for Reeve M. Bailey, curator of fish at the University of Michigan Museum of Zoology 1944-1981.
As described above, emerald darters are sexually dimorphic with males exhibiting more splendid and varied colors than females. Colors reach highest saturation in May, which indicates the peak month for spawning.
Little else is known about the specific mating systems of this species. Clayton’s (1984) attempts to have captive emerald darters mate for observation were unsuccessful, and information is unavailable regarding mate attraction or defense in the wild.
Mating System: polygynandrous (promiscuous)
Actual spawning of emerald darters has not been observed; although attempts by males to mate with unresponsive females in captivity included swimming from side to side over the female’s back. In the wild, males have been observed in riffles, attempting to mount unresponsive females by approaching from behind or from the side.
Spawning occurs in raceways and riffles. Larger males place themselves in pools near the middle of riffles, likely to encounter the greatest number of females, which tend to utilize the middle of the riffles. Although exact spawning behavior is not known, it is likely that emerald darters would be grouped into Page and Swofford’s (1984) “egg attaching” spawning type, in which the female chooses the location to deposit eggs, is mounted by the male and 1 to 3 adhesive eggs and sperm are released simultaneously through mutual vibration. Eggs are then placed by the female on substrate (rocks or plants).
Clayton (1984) observed a few individual eggs widely spaced on aquarium equipment in captivity, although no spawning had occurred. He suggested that the females most likely attach eggs individually, at some distance apart on rocks like other species within the snubnose darter subgenus.
Clayton (1984) also found that although collected gravid females contained 228 to 864 eggs, the average number of ripe eggs (when collected in May) was only 36. Female emerald darters’ eggs ripen, likely in small batches, from early April to early June. The number of eggs produced is directly proportional to the standard length of the individual.
Gonads reach maximum size in males and females in April and May to coincide with spawning. In addition, genital papillae of both sexes become larger and tubular beginning in late March. Clayton (1984) observed that all individuals of one year of age were in spawning condition when collected in May. He therefore concluded that most spawning activity occurs in May. Water temperature affects the length of the spawning season—-- unseasonably warm temperatures may cause females to become unreceptive and to reabsorb eggs earlier in the season than during mild years.
Breeding interval: several times during breeding season
Breeding season: April to June
Average number of offspring: 36.
Range gestation period: 172 to 384 hours.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
If emerald darters are indeed accurately placed in the “egg attaching” group described by Page and Swofford (1984), once the eggs are placed by the female, no further care is given.
Parental Investment: no parental involvement
The emerald darter (Etheostoma baileyi), is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches.[2] It is found only in northern and eastern Kentucky and northeastern Tennessee.
The emerald darter males are generally slightly larger and are more dramatically colored than females, with green accents on various parts of their bodies.[3] Emerald darters can be found in rocky pools of small to medium creeks and rivers that maintain temperatures ranging from 0 to 25 °C.[4]
The emerald darter is restricted to the Cumberland Plateau, including only the upper Cumberland River drainages in eastern Kentucky and northeastern Tennessee. Rivers where emerald darters can be found include the Red River, Jacks Creek, Indian Creek in Kentucky, and Clear Creek, Elk Creek, Poor Creek, and other small water systems. Though populations have fluctuated through the years, the emerald darter's geographic range has stayed the same, and in some areas they can even be found in abundance.[5] Populations may have experienced declines in the past due to strip-mining and siltation in the gravel substrates in which it spawns.[1]
Emerald darters compete heavily with other benthic freshwater fish in the southeastern United States. They are known as opportunistic feeders, relying on food and prey availability which fluctuates drastically throughout seasonal changes. Emerald darters are primarily insectivorous, and depending on size class, 80% to 100% of their diets can consist of small invertebrates. Emerald darters can be found in a variety of clear freshwater habitats with moderately low siltation. The fish can generally be found in water that ranges from 8 to 45 cm in depth, though they are known to retreat to deeper, rock-lined pools during colder months and when floods alter current velocity. Emerald darters inhabit waters that range from 0 to 25 °C, and can be found in riffles and runways up to 0.61 m/s flow velocity.[6] As suggested by the emerald darter's subterminal mouth, they are benthic feeders, primarily consuming small invertebrates such as microcrustaceans, various types of larvae, and nematodes. Emerald darters tend to feed during the day, and their diets largely depend on the time of year, as prey availability changes due to season.[4] They prefer streams with open sunlight and dense vegetation. No predators of emerald darters are known, and their cryptic coloration may help to conceal them in riffles with brightly colored rocks.[7]
Emerald darters spawn in late April and early May. Though actual spawning has not been observed, attempts by males to mate include swimming from side to side over the female's back. Further, males have been observed in the wild trying to mount unresponsive females from behind or from the side. Emerald darter larvae usually measure 4.5 to 6.0 mm in length and emerge from the egg with yolk sacs still attached. Water temperature has a direct correlation with juvenile development, with warmer water temperatures resulting in a faster development and smaller sizes. Warmer temperatures can have even more detrimental effects on populations. Warmer temperatures in the later weeks of the breeding season can cause females to reabsorb their eggs and become unreceptive. Spawning occurs in the center of riffles. Larger males place themselves in pools near the middle of these turbulent areas so they will have a higher probability of encountering more females, which tend to use these areas. Emerald darters prefer gravel substrates that lack silt. Eggs and sperm are released simultaneously through mutual vibration and are attached by the female directly onto the gravel substrate.[8] Emerald darters generally average 36 offspring per year. Most captured emerald darters have been aged at up to three years old. In the Red River drainage, 53% of the population survived its second year, while only 7.7% survived the third. Third-year individuals were predominantly male.[7]
The emerald darter is not currently listed as a state or federal threatened species, though they are experiencing population declines in Tennessee. Though emerald darters have experienced population fragmentation, their range has not undergone declines. Threats to populations include limited range, as well as strip-mining, which results in heavy siltation of the gravel substrates on which they depend for reproduction.[9] Damming of Tennessee's main waterways has fragmented the emerald darter's habitat. Kentucky's populations are not considered threatened.[10]
Management implications would include buffer areas around streams and wetlands to prevent deforestation. This would assist in the prevention of siltation in gravel substrates. More responsible coal practices or eliminating strip-mining altogether will have obvious effects on streams known to contain populations of emerald darters. Strategies such as these are imperative to the conservation of E. baileyi because even localized destruction of its habitat could have devastating effects on its populations.[11] Unfortunately, emerald darters’ benthic feeding habits make this species significantly more susceptible to alterations in habitat.[12]
The emerald darter was first formally described in 1982 by Lawrence M. Page and Brooks Burr with the type locality being given as the Little Sexton Creek which is a tributary of the South Fork Kentucky River in Clay County, Kentucky.[13] The specific name honours the American ichthyologist Reeve Maclaren Bailey (1911–2011) who was Curator Emeritus of Fishes and Professor Emeritus of Zoology, University of Michigan, Museum of Zoology, Ann Arbor, Michigan in recognition of his contribution to systematic ichthyology.[14] The emerald darter has been classified in the subgenus Ulocentra, the snubnose darters and shares many similarities with other species in the group, such as eight or nine dorsal saddles, a blunt nose, scales on the belly, and other distinguishing characteristics. Emerald darters are moderate-sized darters, ranging from 2.9 to 5.0 cm.[15] However, molecular phylogenies have not recovered much evidence of paraphyly within the genus Etheostoma and thus the evidence supporting the use of subgenera for taxonomy in this genus is not strong.[16]
Phillips B.W., C.E. Johnson. "Fish Assemblage Recovery and Persistence." Ecology of Freshwater Fishes (2004): 145-153.
The emerald darter (Etheostoma baileyi), is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is found only in northern and eastern Kentucky and northeastern Tennessee.
