Taxonomy & naming
Elassoma okatie was described by Fred Rohde and Rudolf Arndt in 1987, in a paper introducing two new pygmy sunfishes from the Carolinas, published in the Proceedings of the Academy of Natural Sciences of Philadelphia. It belongs to Elassoma, the only genus in the family Elassomatidae, and no synonyms or subspecies have been proposed for it since.
The family's placement among the ray-finned fishes has moved around. Elassomatidae has traditionally been allied with the sunfishes, family Centrarchidae, on the strength of shared range and a broadly similar body plan, and some older classifications folded the pygmy sunfishes into Centrarchidae outright. The two groups are not closely comparable in scale — an adult pygmy sunfish is smaller than the fry of most centrarchids — and molecular studies have proposed other positions for Elassomatidae among the acanthomorph fishes. The question remains unsettled, and Elassoma okatie is best treated as a member of its own small family rather than as a miniature centrarchid.
Morphology
The bluebarred pygmy sunfish is tiny even by the standards of its genus, reaching at most about 1 in standard length — Georgia state accounts put the ceiling at 1 in, while FishBase lists a maximum of 1.5 in. The body is laterally compressed with a noticeably deep caudal peduncle, the head is unscaled on top, and the mouth is small and terminal to slightly upturned. The caudal fin is rounded rather than forked or notched, and like every other member of the genus, Elassoma okatie has no lateral line — an absence that is diagnostic for the family.
Base coloration is 8 to 14, usually 10 or 11, wide black vertical bars running down each flank, each bar roughly three times the width of the pale interspace beside it, with no large dark blotches on the upper body. That pattern reads very differently depending on sex and season. Females and nonbreeding fish stay a camouflaging beige-brown year-round, while breeding males darken toward black and the bars flush with iridescent blue, the contrast that gives the species its common name.
Habitat
The species is a narrow-range endemic of the Edisto, New, and Savannah River drainages of South Carolina, with an outlying population across the state line on the Fort Gordon military reservation in the upper Coastal Plain of Georgia. It lives in slow-moving to stagnant water — roadside ditches, impoundments, sloughs, creeks, and river backwaters — heavily choked with aquatic vegetation such as alligator weed, bladderwort, and pondweed.
These waters are tea-stained and acidic, typical of the blackwater Coastal Plain, and the fish appears to depend on the vegetation itself for both cover and foraging. A cool overwintering period of roughly 50–59 °F for several weeks is treated as necessary for breeding success in captivity, matching the seasonal cooling these habitats undergo each winter.
Feeding
Elassoma okatie is a micropredator that hunts small crustaceans and aquatic insect larvae among the vegetation it lives in. No dedicated diet study has been published for the species, and its feeding habits are inferred from closely related pygmy sunfishes, but the general pattern — picking tiny invertebrates one at a time off plant surfaces — matches what is known across the genus.
In the aquarium it needs live or frozen foods: California blackworms, daphnia, Grindal worms, and microworms are all reported to work well. Crushed flake is sometimes accepted but should not be relied on as a primary diet, and some individuals can be trained to hand-feed, which tends to make them bolder and less skittish than fish left to forage on their own.
Mating
Spawning takes place in spring. Males stake out small territories in dense vegetation and defend them against rival males and against females that are not yet ready to spawn. Courtship centers on a display described as a "wiggle-waggle" dance — the male undulates his fins and darkens his body in front of a receptive female, drawing her into his territory among the plants.
Breeding coloration is at its most intense during this display: the male's flanks go nearly black and the vertical bars flash iridescent blue, a signal that is largely absent outside the breeding season.
Breeding
Eggs are adhesive and are deposited in the male's territory, attached by fine strands to the stems of submerged plants rather than laid in a nest or scattered freely. Clutch size has not been documented specifically for Elassoma okatie; related species in the genus are reported to lay roughly 50 to 200 eggs per spawning bout, and a similar range is plausible here, though this remains an inference rather than a measured figure for this species.
Beyond guarding his territory during courtship, the male provides no documented care of the eggs or fry once spawning is complete, and incubation time has not been reported in the available literature. Fish reach sexual maturity within their first year, and most individuals do not survive past their second — a short lifespan that makes each spring's spawning effort close to a once-in-a-lifetime event for most fish.
In the aquarium
The natural need for a cool winter dip makes Elassoma okatie a poor candidate for a standard heated community tank and a good one for an unheated species setup kept at room temperature, ideally with a genuine seasonal cool-down if breeding is the goal. Dense planting is essential — the fish spend their lives picking through vegetation and are far more likely to feed and display naturally in a heavily planted tank, such as one thick with Java moss, than a bare one.
Live or frozen foods are close to mandatory; a diet of dry food alone is unlikely to sustain this species long-term. Its small size and inoffensive nature rule out almost every conventional community fish as a tankmate — anything large enough to notice it will eventually eat it — and keepers generally do best pairing it only with shrimp, snails, or other pygmy sunfishes, or keeping it alone. This is not a community fish, and treating it as one is the most common way the hobby loses these fish.
Conservation
Elassoma okatie is assessed as Vulnerable on the IUCN Red List, an assessment dated November 2011. It carries no federal Endangered Species Act listing but is recognized as a federal species of concern; South Carolina lists it as vulnerable at the state level, and Georgia — where it is known only from the restricted Fort Gordon population — lists it as state endangered.
The species' entire range is confined to a handful of drainages between the Edisto and Savannah Rivers, which makes it inherently susceptible to habitat loss. Threats are not documented in fine detail for this species specifically, but the general pressures on its habitat type — wetland drainage, water-quality degradation, and development within the Coastal Plain — are consistent with its restricted range and its Vulnerable status.