Etheostoma baileyi
Emerald darter

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. (Clayton, 1984; Kuehne and Barbour, 1983; Page and Burr, 1991)

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. (Clayton, 1984; Kuehne and Barbour, 1983; Page and Swofford, 1984)

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. (Clayton, 1984; Kuehne and Barbour, 1983; Page and Burr, 1991)

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. (Clayton, 1984; Kuehne and Barbour, 1983)

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. (Clayton, 1984; Etnier and Starnes, 1993; Kuehne and Barbour, 1983)

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. (Clayton, 1984; Kuehne and Barbour, 1983)

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. (Clayton, 1984; Etnier and Starnes, 1993; Kuehne and Barbour, 1983)

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. (Clayton, 1984; Kuehne and Barbour, 1983; Page and Burr, 1991)

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. (Kuehne and Barbour, 1983)

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. (Clayton, 1984; Etnier and Starnes, 1993; Page and Burr, 1991)

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. (Clayton, 1984)

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. (Clayton, 1984; Etnier and Starnes, 1993)

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. (Kuehne and Barbour, 1983)

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. (Clayton, 1984)

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. (Clayton, 1984)

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; Page and Swofford, 1984)

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. (Clayton, 1984)

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. (Clayton, 1984)

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. (Page and Swofford, 1984)

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. (Clayton, 1984)

Little is known about the behavior of emerald darters. It is likely that males are territorial since the only darter species that have not demonstrated territoriality are species in which the females are larger than the males. (Clayton, 1984)

Emerald darters migrate short distances, both upstream and downstream, to deeper pools with cooler fall temperatures in late September to late October. They return to raceways and riffles in March and remain there throughout warm weather. (Clayton, 1984)

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. (Page and Swofford, 1984)

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. (Clayton, 1984)

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. (Page and Swofford, 1984)

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. (Clayton, 1984)

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 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. (Etnier and Starnes, 1993; Kuehne and Barbour, 1983)

Etheostoma baileyi was named for Reeve M. Bailey, curator of fish at the University of Michigan Museum of Zoology 1944-1981. (Kuehne and Barbour, 1983)