Taxonomy & naming
The Dutch ichthyologists Max Weber and Lieven de Beaufort described this fish in 1922. Eschmeyer's Catalog of Fishes records the valid name as Telmatherina bonti Weber & de Beaufort, 1922 — retained in its original genus, and so carrying no parenthetical authority. It belongs not to the true rainbowfishes (Melanotaeniidae) but to the family Telmatherinidae, the sailfin silversides, within the order Atheriniformes. Some aquarium sources misfile it under Melanotaeniidae; this atlas follows the Catalog of Fishes and FishBase, which place it among the telmatherinids.
The genus name joins the Greek telma (genitive telmatos), swamp or marsh, with atherina, the classical name for the silverside or smelt — a 'silverside of the swamps.' The epithet bonti is not an eponym. It comes from the Sulawesi name for these fish, 'bonti-bonti,' still used in the hobby today. The Telmatherinidae are a small family centred almost entirely on Sulawesi, and the Malili lakes host a species flock of Telmatherina and allied genera that has drawn evolutionary biologists for decades.
Meristic characters reported for the species include 8 to 10 soft dorsal rays, a single anal spine, and 10 to 13 anal soft rays, with a 1/2 6 1/2 scale count in a transverse row. These are the fine characters used to separate members of the Malili flock, where body shape and colour vary considerably between populations.
Morphology
Telmatherina bonti is a small, fusiform sailfin silverside reaching about 2.5 in in standard length. Within the Malili telmatherinids it stands out for a bulkier, more robust build. FishBase describes a broken dorsal profile with a shallow hump on the nape, giving mature fish a slightly arched, heavier-headed look than the slender, more typically silverside-shaped members of the flock.
As in other sailfin silversides, the body is laterally compressed and silvery, with the family's two separated dorsal fins and an elongate anal fin. 'Sailfin' refers to the enlarged, sometimes filamentous unpaired fins that displaying males carry. The genus Telmatherina is known across the Malili lakes for colour polymorphism — populations and individuals vary in fin and body hue — and T. bonti shares in this variability, though it ranks among the plainer, more silvery members rather than the brilliantly coloured forms.
Colour descriptions specific to this species are sparse in the primary literature, and much of what circulates in the hobby blends observations across the closely related Malili sailfins. Preferring restraint to guesswork, the safest statement is this: a silvery, robust-bodied sailfin silverside of modest size, with the broken dorsal profile and nape hump as its most diagnostic external features.
Habitat
Telmatherina bonti is endemic to the Malili lakes system of central Sulawesi, Indonesia — a cluster of ancient tectonic lakes that includes Lake Towuti, Lake Mahalona, and Lake Matano. FishBase records it from Lake Towuti and the vicinity of Malili, as well as Lake Mahalona, placing it among the freshwater fauna found nowhere else on Earth. These are tropical waters, lying roughly 1 to 3 degrees south of the equator.
The Malili lakes are old, deep, and chemically distinctive. Their catchments are rich in ultramafic (ophiolite) rock, and the water is hard and decidedly alkaline, with pH above 8. An importer's field note for this species stresses that the lake water is always rather warm — on the order of 28 degrees Celsius — and consistently alkaline, a useful corrective to the cooler 22 to 24 degree figure carried in some general databases. The species is non-migratory, leans pelagic, and tolerates a wide hardness range.
Clear, warm, alkaline, mineral-rich water in a closed ancient-lake basin is what makes the Malili system such a productive site of in-lake speciation. It is also what makes its endemics, T. bonti among them, so vulnerable: there is essentially nowhere else for them to live.
Feeding
Telmatherina bonti is an omnivore with a reported trophic level of about 3.1, feeding in the water column on small animal prey. In the wild the Malili sailfin silversides take small invertebrates and insects, snails, and — a striking habit of this species flock — the eggs of other fishes, including those of their own relatives. Egg-eating is well documented in the Malili telmatherinids, part of the tangled predator–prey and reproductive interactions inside the lakes.
In captivity it is an undemanding feeder that readily accepts dried foods alongside live and frozen items such as Tubifex, mosquito larvae, and bloodworm. A varied diet weighted toward small invertebrate foods suits its natural ecology and keeps fish in condition.
Given its small size and active habits, feed little and often rather than in large infrequent meals — that matches the steady column-feeding of a silverside in open water.
Mating
Like other sailfin silversides, Telmatherina bonti deposits eggs rather than bearing live young, and hobby observations describe a continuous spawner that breeds over an extended period rather than in a single seasonal burst. Morning sunshine reportedly triggers spawning, with pairs becoming active in the early light — a pattern shared with the rainbowfishes and the broader silverside lineage.
The Malili telmatherinids interest evolutionary biologists largely for their mating systems. The flock shows assortative mating tied to male colour and fin morphology, and this sexual selection is thought to drive the rapid diversification seen within the lakes. Courtship descriptions specific to T. bonti are sparse, so the account here stays general to the genus.
In the aquarium, displaying males court females over fine-leaved plants or spawning mops, dropping eggs a few at a time across the medium rather than laying one large clutch.
Breeding
Telmatherina bonti deposits small numbers of adhesive eggs onto fine-leaved plants or synthetic spawning mops, continuing over many days. As with rainbowfishes, the adults eat their own eggs, so breeders usually move the mops or eggs to a separate rearing container.
Hobby reports give an incubation of roughly 7 to 14 days, shortening in warmer water. The newly hatched fry are tiny and need correspondingly small first foods and clean, stable water. The species is sensitive to poor water quality, and that sensitivity peaks at the fry stage.
Because the natural water is warm and alkaline, condition and spawn the fish in hard, alkaline water in the upper twenties Celsius — not the soft, cooler conditions sometimes assumed for tropical egg-scatterers. Beyond these broad points, species-specific breeding data are limited, and prospective breeders should expect to work largely from general telmatherinid practice.
In the aquarium
This is an intermediate-difficulty fish: peaceful and rather shy, with delicate fins that make it a poor companion for fin-nippers. Keep it as a shoal of six to eight or more, with the sex ratio skewed toward females — roughly two or three females per male — to spread male attention and keep the group settled. It works the middle and upper levels of the tank and can live around five years.
The job is to recreate Malili-lake water: hard, distinctly alkaline, warm, with strong filtration, plenty of current, and stable water quality, since the species reacts badly to poor conditions and to common diseases. Hobby guidance points to a pH on the alkaline side and substantial hardness, with a dark sandy substrate showing the fish to best effect. Importer field notes put the lake water consistently warm — around 28 degrees Celsius — and always above pH 8, more reliable than the cooler figures in some general references.
Tankmates should be peaceful and equally happy in water harder and more alkaline than the tropical norm; timid or delicate-finned community fish and active fin-nippers are both poor matches. Given the species' threatened wild status, captive breeding and tank-bred stock are the responsible way to keep it in the hobby.
Conservation
Telmatherina bonti is assessed as Endangered (EN) on the IUCN Red List. The listing reflects an extremely restricted range — a handful of connected ancient lakes in the Malili system — set against documented declines and ongoing threats to that habitat.
The main pressures are overexploitation, destructive fishing, and the introduction of non-native, invasive fishes into the Malili lakes. Introduced predators and competitors hit a small endemic silverside that evolved in isolation especially hard, and the same closed-basin geography that produced the Malili flock leaves its members no outlying populations to buffer local losses. The species has commercial value in both fisheries and the aquarium trade, which adds collecting pressure on top of habitat change.
For a narrowly endemic fish of an ancient-lake system, conservation comes down to the integrity of the lakes themselves — their water quality, their fish communities, and the management of introductions. In the hobby, sourcing captive-bred rather than wild-caught stock cuts direct collecting pressure and helps keep the species going outside its single threatened range.