Taxonomy & naming
Paratherina labiosa was described by Aurich in 1935 and is placed in the family Telmatherinidae, the sailfin silversides, within the order Atheriniformes. Eschmeyer's Catalog of Fishes records the valid name as Paratherina labiosa Aurich, 1935. The genus Paratherina is one of three silverside genera endemic to the Malili Lakes of central Sulawesi, the others being Telmatherina and Tominanga; together with the river-dwelling Marosatherina ladigesi of southwestern Sulawesi they make up the small Indonesian radiation of this family.
The family name points to both the slender, silvery atheriniform body plan and the elaborate fins that males of several genera carry. P. labiosa shares the basic Telmatherinid form — a compressed, translucent-silvery body, a divided dorsal fin, the upturned mouth of a surface- and midwater-feeder. But the literature on the species itself is thin. Telling the Malili silversides apart comes down to fine differences in fin shape, squamation and coloration, not dramatic external characters.
The generic name is built from the Greek para, meaning near or beside, and atherina, an old Greek name for the smelt or sand-smelt, so Paratherina reads as 'near the silverside' — a name that situates the genus alongside the broader silverside assemblage. The specific epithet labiosa derives from the Latin for 'large-lipped' or 'full-lipped', presumably a reference to a lip character noted in the original description. The principal modern reference treating the species is Kottelat, Whitten, Kartikasari and Wirjoatmodjo's 1993 Freshwater Fishes of Western Indonesia and Sulawesi.
Morphology
Paratherina labiosa is a small fish, reaching a maximum recorded length of about 4 in total length (Kottelat et al. 1993). It has the typical sailfin-silverside build: an elongate, laterally compressed, silvery body that is somewhat translucent in life, a divided dorsal fin set well back, and a small, upturned mouth suited to taking food at and just below the surface.
The family name points to fin development as a defining feature, and the epithet labiosa ('full-lipped') suggests the lips caught the original describer's eye. Published morphometrics for this species are limited, though, so most of what can be said with confidence concerns the family-level body plan rather than traits diagnostic of P. labiosa alone.
Sourced data on coloration, fin counts and sexual differences are sparse for this fish. Rather than borrow details from better-studied relatives, this account flags where the record actually lies: the fine morphology of P. labiosa is documented chiefly in Aurich's 1935 description and in Kottelat and colleagues' regional treatment, and any precise meristic claim should be checked against those.
Habitat
Paratherina labiosa is endemic to Lake Wawontoa (also written Lontoa), a component of the Malili Lakes system in central Sulawesi, Indonesia. The Malili Lakes are a chain of ancient tectonic lakes — Matano, Mahalona and Towuti are the largest — linked by short rivers, and they are renowned among biologists as a hotspot of freshwater endemism. FishBase records the species as a freshwater, pelagic, non-migratory inhabitant of the tropics, living in the open water of the lake rather than in flowing rivers.
The water is clear, mineral-rich, hard and alkaline — a chemistry inherited from the ultramafic and limestone geology of the catchment. These are the conditions that drive in-situ radiations: stable, deep, clear water over geological timescales, with distinct genera evolving to partition the open water and littoral zones. P. labiosa is one product of that long isolation, found here and nowhere else.
That confinement is the central fact of its ecology. A fish penned into one small lake has no refuge population to fall back on, so any shift in water quality, any introduced competitor or predator, any change to the lake's hydrology lands on the entire global population at once — the vulnerability behind its conservation status.
Feeding
FishBase places Paratherina labiosa at a trophic level of roughly 3.1, consistent with a small, mid-water omnivore-to-carnivore that takes invertebrate prey. Sailfin silversides of the Malili Lakes generally feed in the open water and at the surface on small invertebrates — insect larvae, zooplankton and drifting insects — using their upturned mouths to take food from the upper water column.
No dietary study of P. labiosa shows up in the available sources, so the account here sits at the genus and family level rather than on direct observation. The open-water, pelagic habit FishBase records for it fits a planktivorous and insectivorous diet.
The fish is essentially absent from the aquarium trade — a threatened single-lake endemic — so there is no hobbyist husbandry literature to lean on for captive feeding. Where the data are thin, this profile says so rather than invent a diet the sources don't support.
Mating
The reproductive behaviour of Paratherina labiosa is poorly documented. Sailfin silversides are egg-layers, and in several related Malili-Lakes genera the males grow enhanced fins and display and court in the littoral and open-water zones — but no record of pairing or courtship for this species turns up in the available material.
Rather than borrow details from Telmatherina or other relatives: on present evidence the mating system of P. labiosa is simply unstudied at the level a confident description would need. A restricted range and no commercial interest have left it far less examined than the colourful, hobby-popular Marosatherina ladigesi of southwestern Sulawesi.
As an atheriniform of an ancient-lake radiation it almost certainly reproduces by external fertilization, with adhesive eggs deposited in the environment — the general family pattern. Timing, site selection and any display behaviour still wait on primary observation.
Breeding
No detailed breeding account for Paratherina labiosa appears in the sources, and the species has never settled into the hobby the way egg-laying sailfin silversides like the Celebes rainbowfish (Marosatherina ladigesi) have. Telmatherinid silversides typically lay small numbers of adhesive eggs that stick to vegetation or substrate, with no parental care — but pinning that on P. labiosa would go past what the sources support.
Given the Critically Endangered status and single-lake range, captive breeding could in principle do conservation work, as it has for other threatened Sulawesi endemics. But no breeding programme or aquarium-spawning record for P. labiosa turns up in the material reviewed here, which keeps this section short.
The breeding biology of this fish is, for now, essentially undescribed in accessible literature. Anyone meaning to work with it for conservation would have to start from the family-level pattern and from field study of the Malili Lakes silversides — there is no established protocol for this particular species to follow.
In the aquarium
Paratherina labiosa is not a trade fish. The Celebes rainbowfish (Marosatherina ladigesi), bright and sailfin-finned, is widely kept; the Malili-Lakes Paratherina silversides are rarely if ever exported and sit outside normal ornamental commerce. As a Critically Endangered single-lake endemic, this is a wild species of conservation concern, not a hobby fish.
What husbandry-relevant detail the sources offer comes down to water chemistry. The Malili Lakes are clear, hard and alkaline, so any captive maintenance for conservation would have to match that mineral-rich, alkaline water — not the soft, acidic conditions assumed for many tropical fishes. Temperature would track the warm lake.
With no body of hobbyist experience behind it, no care rating or stocking advice can be offered with confidence, and this profile won't invent one. Aquarists drawn to Sulawesi sailfin silversides are far likelier to find — and far better off keeping — the trade-available Marosatherina ladigesi, leaving the threatened Paratherina species to managed conservation work.
Conservation
The IUCN Red List assesses Paratherina labiosa as Critically Endangered under criteria B1ab(iii). The listing turns on its range restriction — endemic to one small lake within the Malili Lakes system — and an inferred continuing decline in habitat quality. A fish confined to a single lake has, by definition, an extent of occurrence and area of occupancy small enough to clear the geographic thresholds for the highest threat categories.
The pressures are the familiar ones for small, isolated tropical lakes under development: habitat degradation, sedimentation and water-quality changes from catchment activity, and non-native fishes introduced to prey on or compete with the natives. For an endemic with no outlying population, each pressure hits the whole species at once — the reason the Malili silversides as a group rank as a conservation concern.
So the conservation of P. labiosa can't be separated from the conservation of its lake. Protect the water body — its chemistry, its hydrology, its native fish community — and you protect the species; there is nowhere else to fall back on. Groups working on Sulawesi's endemic freshwater fauna single out the Malili silversides for exactly this reason: their ranges leave almost no margin for error.