Taxonomy & naming
The Swiss ichthyologist Maurice Kottelat described Tominanga sanguicauda in 1990, out of his work on the freshwater fishes of the Malili lake system in central Sulawesi, Indonesia. It belongs to the Telmatherinidae, the sailfin silversides — small atheriniform fishes that, like the rainbowfishes proper, have thrown off many endemic forms within Sulawesi's fresh waters. Eschmeyer's Catalog of Fishes records the valid name as Tominanga sanguicauda Kottelat, 1990, the authority without parentheses because the species still sits in the genus where it was first placed.
The genus Tominanga holds only two species — T. sanguicauda and its congener T. aurea — and takes its name from the Tominanga river of Sulawesi. The epithet comes from the Latin sanguis, 'blood', and cauda, 'tail': the red caudal fin of the living male. Two characters separate the species. T. sanguicauda bears 27 to 31 gill rakers on the first arch against 31 to 36 in T. aurea, and its body in life may be plain blue or red, with the dorsal, anal and pelvic fins blue or red and the tail always red.
Morphology
A small, slender silverside. FishBase records a maximum length of about 2 in SL; a 2024 field study at Lake Towuti measured males at roughly 2–2.5 in total length and females at about 1.5–2 in — males plainly the larger sex. Reported meristics run to 9 to 11 dorsal soft rays, a single anal spine, and 12 to 14 anal soft rays.
The living male's colour gives the fish both its name and its appeal. The body may be plain blue or red, the dorsal, anal and pelvic fins matching, the caudal fin always red — the 'blood tail' of sanguicauda. On hard characters, what separates it from its only congener, T. aurea, is the lower first-arch gill-raker count of 27 to 31. As with most small endemic silversides, the bony characters overlap with relatives, so live colour is among the more reliable field marks.
Habitat
Tominanga sanguicauda is endemic to Lake Towuti, the largest lake of the Malili complex in East Luwu, South Sulawesi, Indonesia. Towuti is an ancient, oligotrophic tectonic lake covering some 561 square kilometres, one of a chain of geologically old lakes that has driven the in-lake speciation seen across Sulawesi's sailfin silversides, shrimps and snails. FishBase characterises the environment as tropical freshwater — with some tolerance of brackish conditions — at temperatures around 68–79 °F.
Field sampling reported in 2024 collected the species along the lake's margins at several capes, including Tanjung Bakara, Tanjung Saone and Tanjung Tominanga on the eastern and southern shores. There it shares the water with other Towuti endemics and residents: the sailfin silversides Telmatherina and Paratherina, gobies such as Glossogobius and Mugilogobius, the halfbeak Dermogenys, ricefishes of the genus Oryzias, and its own congener Tominanga aurea. The whole of its world range is this one ancient lake — the central fact of both its biology and its conservation.
Feeding
An omnivore. A 2024 study of condition factors and food habits at Lake Towuti found relative gut lengths between roughly 1.0 and 1.2 — a ratio in the range (between 1 and 3) that points to omnivory rather than strict carnivory or herbivory.
Stomach contents in that study were dominated by a single aquatic insect, the shore-bug or waterbug Ochterus (Ochterra) humilis, which made up roughly a fifth of the gut, alongside a broad assemblage of diatoms and algae — among them Skeletonema, Chlorella, Synedra, Anabaena, Thalassionema, Coscinodiscus, Navicula, Rhizosolenia, Merismopedia and Diatoma. Condition factors from the same work classed the fish as lean ('flat', not fat), which fits a small, active lake-margin forager. Beyond this one dietary study, ecological data on the species remain sparse.
Mating
Courtship and mating in Tominanga sanguicauda have not been described in any detail, and FishBase carries no reproductive data for the species. What is clear is that the sexes differ sharply: males grow larger than females and take on the blue or red body and red tail of breeding condition, while females stay smaller and plainer. That kind of size and colour dimorphism runs through the sailfin silversides of Sulawesi, in which males show off their fins and colours to females.
Given the thin published record, the finer points of pair formation, spawning-site choice and seasonality are better left as data-sparse than guessed at. Behaviour is presumed broadly similar to that of related Sulawesi silversides, but no specific courtship description for T. sanguicauda exists in the literature available here.
Breeding
Breeding biology specific to Tominanga sanguicauda is poorly documented; spawning mode, egg size, clutch size and incubation time are all absent from the standard reference databases. The size gap between the sexes — males substantially larger — is the clearest reproductive signal in the available data.
Sailfin silversides as a group are egg-layers whose adhesive eggs attach by fine filaments to vegetation or substrate, and Sulawesi telmatherinids tend to breed continuously rather than seasonally in their stable tropical lakes. Whether T. sanguicauda follows that pattern has not been confirmed in the literature consulted, so its breeding habits are noted here as sparse rather than asserted. This is a wild endemic of little aquarium presence, and there are no captive-breeding accounts to draw on.
In the aquarium
Tominanga sanguicauda is not a fixture of the ornamental trade and is rarely if ever kept; it is far better known to ichthyologists working on Sulawesi's endemic fishes than to aquarists. As a restricted-range endemic of a single threatened lake, it makes a poor candidate for casual collection, and there is no body of husbandry experience to lean on.
What little can be said follows from the habitat, not from hobby tradition. This is a small, active shoaling silverside from clear, mineral-rich, slightly alkaline-leaning water at roughly 68–79 °F; it would want those conditions, open swimming space and a group of its own kind to behave normally. Because the fish is wild-caught from a Near Threatened population, the honest answer is that it belongs in the lake and in scientific care rather than in the trade.
Conservation
Tominanga sanguicauda is assessed as Near Threatened (NT) on the IUCN Red List, under criteria B1b(iii)+2b(iii). The assessment was carried out on 14 June 2018 and published in 2019 (Lumbantobing, assessment e.T21980A90980344). The listing rests on the restricted range — Lake Towuti alone — set against a continuing decline in habitat quality.
The documented threats to the fish and its lake are introduced and invasive species, habitat perturbation and degradation, destructive fishing, and over-exploitation. A single-lake endemic has no outlying population to absorb such pressures, so disturbance within Towuti translates straight into risk for the whole species. The 2024 field study likewise noted a population decline over the preceding decade, blamed on the same forces. So the fate of T. sanguicauda is inseparable from that of Lake Towuti and the wider Malili system, one of the most distinctive ancient-lake faunas anywhere.