Taxonomy & naming
Lebiasina bimaculata was originally described by Achille Valenciennes in 1847. It belongs to the family Lebiasinidae, a South American lineage of small to medium-sized characiforms that includes the pencilfish (Nannostomus), the pencilfishes (Nannostomus), and other splash tetras. Within Lebiasinidae the genus Lebiasina is placed in the subfamily Lebiasininae and contains around a dozen recognised species distributed across Pacific-slope and trans-Andean freshwaters of Colombia, Ecuador, and Peru.
The species epithet bimaculata is Latin for 'two-spotted', referring to the two dark spots — a humeral spot behind the operculum and a spot at the caudal peduncle base — that mark the fish's flanks. Catalogue of Fishes records the valid name as Lebiasina bimaculata Valenciennes, 1847. Common names in use include Twospot Lebiasina and Twospotted Lebiasina in English; in coastal Ecuador the fish is widely known as huaija (also spelled guaija), and the name kurumby is recorded in some Spanish-language sources.
Morphology
Lebiasina bimaculata is a moderately elongate, somewhat stocky fish reaching a maximum recorded standard length of 6.5 in, though most individuals encountered in the field or aquarium are considerably smaller. The body is cylindrical to slightly compressed, with a rounded snout and a terminal to slightly upturned mouth consistent with surface-feeding habits. One notable morphological peculiarity of the species is that the majority of individuals lack an adipose fin — the small rayless fin characteristic of most characins — making its absence here a diagnostic point rather than an abnormality.
The most distinctive colour features are a bright red or orange-red spot on the lateral line in the mid-body region, a dark humeral spot immediately behind the head, and a second dark spot at the base of the caudal fin. These markings are most vivid in healthy, well-fed fish under good lighting. The overall base colour is a warm olive-bronze to tan, with the flanks sometimes showing a subtle iridescence. Females tend to be fuller-bodied when gravid, but sexing outside of reproductive condition is not straightforward.
Habitat
In the wild, Lebiasina bimaculata occupies the Pacific-slope river systems of western Ecuador — from the Esmeraldas drainage in the north to El Oro province near the Peruvian border — and continues south into the coastal and trans-Andean drainages of Peru including the Marañón basin. It is a fish of lowland and foothill streams, showing a strong preference for stagnant or slow-moving marginal pools along stream edges, backwaters, and ditches rather than the main channel.
The key ecological characteristic of this species is its extraordinary tolerance of hypoxic water, enabled by facultative air-breathing. It regularly inhabits standing pools where dissolved oxygen is severely depleted and few other fishes can survive. Water parameters across its range broadly span 72–79 °F and pH 6.2–7.5, though it can persist in conditions outside these ranges. This hardiness underlies both its success as a mosquito-control introduction and its resilience as an aquarium fish.
Feeding
Lebiasina bimaculata is primarily insectivorous in the wild, with surface-feeding behaviour documented across its range. It takes aquatic and terrestrial insects, small invertebrates, and stream invertebrates near the water surface; the upward-oriented mouth is well suited to snatching prey from the film or just below it. The DePaul University freshwater fishes survey for western Ecuador describes it as broadly omnivorous, incorporating plant material and small invertebrates opportunistically.
This surface-feeding bias made the species attractive as a biological control agent, as mosquito larvae and pupae congregate near the water surface. In captivity it accepts most standard aquarium foods including flake, small pellets, and frozen or live invertebrates such as bloodworm, Daphnia, and brine shrimp. Feeding at or near the surface suits its natural posture, and sinking foods may be ignored unless the fish is hungry.
Mating
Lebiasina bimaculata belongs to Lebiasinidae, a family that encompasses a range of reproductive strategies from simple egg-scattering to the elaborate terrestrial spawning of Copella arnoldi, the splash tetra. Within the genus Lebiasina the evidence points to egg-laying with minimal parental investment, consistent with the broader Lebiasininae pattern of depositing eggs among vegetation or substrate.
Male courtship in the genus typically involves pursuit and lateral display alongside a receptive female. The species does not practise the guardian brood-care seen in some related pencilfish; spawning is not thought to involve the male splashing behaviour characteristic of Copella. Detailed field observations of mating behaviour in the wild are sparse in the available literature.
Breeding
Lebiasina bimaculata is an egg-layer that can be induced to spawn in captivity, though detailed breeding reports in the hobby literature are less abundant than for more commonly kept characins. General Lebiasinidae breeding data indicate clutch sizes of 1–100 eggs depending on species, with eggs settling to the substrate or adhering to fine-leaved plants, and incubation times of one to four days at tropical temperatures.
For Lebiasina specifically, a conditioning period with live or frozen foods, slightly raised temperature, and the provision of fine-leaved plants or spawning mops is the recommended approach. The adults will consume eggs and fry if left in contact with them, so eggs or spawning medium should be removed to a separate rearing vessel. Fry are small at hatching and require infusoria or commercial liquid fry food before graduating to newly hatched brine shrimp. Captive-bred stock is rarely available commercially, meaning most aquarium specimens are wild-caught.
In the aquarium
Lebiasina bimaculata is an exceptionally hardy aquarium fish whose tolerance of poor water quality and low oxygen stands apart from most commonly kept tropical species. It does not require the pristine, well-oxygenated water demanded by many tetras and can endure temporary lapses in maintenance that would stress more sensitive tankmates. A tank of 23.5–31.5 in in length is adequate for a small group; it is not an especially active open-water swimmer and spends much of its time in the mid to lower strata or cruising near the surface.
The species can be kept in community tanks with similarly sized, robust fish, though its surface-feeding habit and moderate size mean smaller or more timid tankmates may be outcompeted. Water temperature in the range of 72–79 °F suits it well, with pH around 6.5–7.5. A well-planted tank with some surface cover reduces stress. Because most specimens are wild-caught, a period of quarantine and conditioning on varied live and frozen foods before introduction to the display tank is advisable. The fish is not widely stocked in the trade but surfaces periodically through specialist importers.
Conservation
Lebiasina bimaculata is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment completed on 24 September 2020. The species' widespread distribution across Pacific-slope and trans-Andean drainages of Ecuador and Peru, combined with its tolerance of degraded habitats, supports this relatively secure status despite ongoing pressures on freshwater ecosystems across its range.
One conservation complexity arises from the species' history as a deliberate introduction for mosquito larval control. It has been released into drainages and water bodies beyond its native range, including on other continents, where its impact on native invertebrate and fish communities has not been fully assessed. The U.S. Fish and Wildlife Service records it as a species with uses in commercial fisheries, the aquarium trade, and as bait, reflecting the multiple human interactions with this adaptable fish. Monitoring of introduced populations and their ecological effects represents an ongoing conservation consideration.