Taxonomy & naming
Telmatherina abendanoni was described by the Dutch zoologist Max Weber in 1913, among the sailfin silversides of the ancient Malili lakes system of central Sulawesi. Eschmeyer's Catalog of Fishes records the valid name as Telmatherina abendanoni Weber, 1913; the species has remained in Telmatherina, the type genus of the family Telmatherinidae, and so carries no parenthetical authority. The family sits within the order Atheriniformes, the silversides, and its members are small, often slender, surface- and mid-water fishes of the Indo-Australian region.
The genus Telmatherina is largely a Lake Matano endemic radiation, with roughly nine to ten described species sharing the lake and the wider Malili system. T. abendanoni lives alongside relatives such as T. antoniae, T. sarasinorum, T. opudi, T. wahjui and T. prognatha. Herder, Pfaender, Schliewen and colleagues have studied the group intensively as a model of how closely related forms partition habitat, diet and mating within one body of water. T. abendanoni stands out by its larger maximum size and an odd gill-raker condition: rakers that are normally developed in small fish shrink to little more than a short knob in most large adults.
Morphology
Telmatherina abendanoni is the largest of the Lake Matano telmatherinids, reaching about 2.5 in standard length; the largest known specimen measured 2.5 in SL. It has the slender, laterally compressed body typical of the sailfin silversides, with the family's two dorsal fins and, in this species, pointed anal and second dorsal fins. In an ecological survey of the lake, specimens taken in rocky habitat ranged from roughly 2–3 in total length and weighed between about 0.9 and 5 grams.
The species is most reliably separated from its congeners (T. opudi, T. sarasinorum, T. wahjui and T. obscura) by its greater length and by the reduced gill rakers of large individuals: where small fish carry normally developed rakers, these shrink to a short knob as the fish grows. Detailed live-colour data for T. abendanoni are sparse in the sources at hand; like other Telmatherina it is expected to show some male display colour and fin development, but specifics are not asserted here beyond what the literature supports.
Habitat
Telmatherina abendanoni is endemic to Lake Matano in South Sulawesi, Indonesia — a deep, ancient, oligotrophic lake within the Malili lakes system, at roughly 2 to 3 degrees south of the equator. The water is clear and nutrient-poor, and the lake is old enough and isolated enough to have generated its own endemic fauna, of which the Telmatherina flock is the best-studied part. The fish is freshwater, non-migratory, and broadly pelagic within the littoral zone.
Within the lake, T. abendanoni favours the rocky and riparian littoral margins. In a habitat-composition study of the lake's Telmatherina it was found mainly on rocky and root/trunk substrates of the shoreline, generally in areas without aquatic plants. It is scarce: it made up only 18 of 415 Telmatherina specimens captured (about 4.3 percent overall, and roughly 7 percent of the rocky-habitat catch), so even where present it occurs in small numbers alongside more abundant congeners.
Feeding
Telmatherina in Lake Matano are carnivorous, and the ecological literature places T. abendanoni among the predatory members of the flock, taking arthropods and small fish; FishBase places the species at a trophic level of about 3.1. Litter and detritus are reported as complementary food, but invertebrate and fish prey form the core of the diet.
The Matano sailfins partition their food and space: different species and forms specialise on different prey and microhabitats, which is part of why so many closely related Telmatherina coexist in one lake. The reduced gill rakers of large T. abendanoni fit a more predatory habit than the finer-raker, more particulate-feeding strategy seen in some relatives — though the sources here describe the diet rather than tying it mechanistically to raker form.
Mating
Evolutionary biologists know the Lake Matano Telmatherina for their mating behaviour, which is thought to drive the radiation through sexual selection and assortative mating among colour and habitat forms. Courtship specific to T. abendanoni is poorly documented in the sources at hand, so only the general genus pattern supported by the literature is given here.
Telmatherina are substrate spawners that deposit adhesive eggs onto surfaces in the littoral zone — the sides of submerged roots, among rocks and gravel, on sandy bottoms, and sometimes on large boulders — typically in places without aquatic vegetation, with the eggs placed at the bottom of the water. Mate choice and microhabitat use are tightly linked in this group, and the interplay between where a fish spawns and which partners it chooses is central to how the Matano flock has diversified.
Breeding
As described for the genus in Lake Matano, Telmatherina lay their eggs on the substrate of the littoral zone rather than scattering them into open water or among floating plants. Reported spawning sites include the sides of riparian roots and trunks, gravel and rocky substrate, sandy bottoms, and occasionally large boulders, generally in areas free of aquatic plants, with eggs settling to the bottom of the water.
Species-specific breeding data for T. abendanoni — clutch sizes, incubation times, parental behaviour — are not well documented in the sources at hand, and are not invented here. The species reproduces within the same narrow littoral habitats it occupies year-round, so its breeding success is tied directly to the rocky and riparian margins of the lake, the zones most affected by shoreline disturbance.
In the aquarium
Telmatherina abendanoni is reported by FishBase as being of commercial interest both as a food fish and in the aquarium trade, and the Matano sailfin silversides as a group have a niche following among specialist keepers drawn to the lake's endemic fauna. It is not, however, a mainstream hobby fish, and detailed, species-specific husbandry information is limited.
The wild habitat sets the brief: this is a fish of clear, oligotrophic, neutral-to-alkaline ancient-lake water, living along open rocky and root-lined margins rather than in densely planted shallows. Mirror those conditions — clean, well-oxygenated water, open swimming space over rock and sand, stable parameters — and keep the fish in a group, as it schools in the littoral zone. Given its restricted range and Near Threatened status, captive-bred stock is preferable to wild-caught. Precise temperature and chemistry targets are not asserted here beyond that general ancient-lake profile, since species-specific aquarium parameters are sparse in the sources.
Conservation
Telmatherina abendanoni is assessed as Near Threatened (NT) on the IUCN Red List (species ID 21571), under criteria B1b(iii,iv,v)+2b(iii,iv,v); the assessment was carried out on 29 June 2018 and published in the 2019 Red List update (Lumbantobing, 2019). The listing reflects the species' confinement to a single small water body — Lake Matano — and the documented pressures on that lake's shoreline and catchment.
The principal threats are land-based: pollution, conversion of land to agriculture (notably pepper cultivation), mining activity in the surrounding region, settlement, and the abrasion and loss of riparian vegetation along the lakeshore. Dam construction altering water flow, habitat fragmentation, and introduced fishes competing for food and space are further stresses on the endemic Telmatherina flock. Because T. abendanoni is both narrowly endemic and naturally uncommon, it has little buffer against habitat degradation. The rocky and riparian margins it depends on for feeding and spawning are exactly the zones most exposed to shoreline development, so protecting Lake Matano's littoral margins is what the species' future turns on.