Telmatherina sarasinorum

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Telmatherina sarasinorum, also known as the Sarasin Rainbow, is a small rainbowfish endemic to Lake Matano on the island of Sulawesi, Indonesia. This species belongs to a highly specialized freshwater fauna that has remained isolated in the ancient lakes of the region for a long time. Its slender body, metallic reflections and delicate fins give it a striking appearance, especially under side lighting. Considered very rare in the aquarium trade, it is best suited to experienced aquarists who can provide warm, clean and stable water. It is available exclusively from Ton.Fish in Canada.

General species description

Telmatherina sarasinorum is a small atheriniform fish from the family Telmatherinidae, recognized by its slender shape and active midwater behavior. The species is endemic to Lake Matano, meaning that its natural range is restricted to this single lake system. It generally lives in groups and uses open shoreline areas, where it searches for small prey in the water column. Successful care requires excellent water quality, good oxygenation and careful acclimation. Its availability remains very rare in the aquarium trade, and specimens should ideally be kept in a group in a spacious, peaceful and fully matured aquarium.

Geographical origin and biotope

Telmatherina sarasinorum comes from Lake Matano in Sulawesi, Indonesia, within the Malili lake system. The lake is a large ancient freshwater body known for its high clarity, tropical temperature and low organic load. Areas used by this species include rocky shorelines, quiet coves and locations where the bottom alternates between stones, sand and plant debris. The water is generally alkaline, warm and well oxygenated. Aquatic vegetation may occur in localized patches rather than forming continuous beds, while the shores are surrounded by Sulawesi’s tropical vegetation. The natural habitat is lacustrine, so water movement is limited to wind-driven movement and local currents.

Precise location and local name

The reference locality for Telmatherina sarasinorum is Lake Matano, in the Malili lake complex of southern Sulawesi, Indonesia. This very restricted distribution explains the species’ scientific and aquarium interest. In the region, fish of the genus Telmatherina are commonly associated with the local name opudi, a term used for several native forms from these lakes rather than exclusively for one species. In aquaria, the English name Sarasin Rainbow is widely used. Like several endemic Matano fishes, Telmatherina sarasinorum deserves careful handling to avoid mixing populations and to preserve the identity of captive-maintained lines.

Appearance and physical characteristics

Telmatherina sarasinorum has an elongated, laterally compressed body, a relatively slender head and large eyes suited to searching for prey. Its flanks may show silver to blue reflections, enhanced by yellowish or golden tones depending on lighting, mood and sex. The fins are transparent to lightly tinted; mature males generally develop stronger contrast and more extended fins than females. The body remains delicate, without the extremely elongated fins seen in some other Telmatherina. The maximum size reported in aquaria is about 8 cm, although commonly seen specimens are often smaller. Clear water and a dark background bring out its iridescence particularly well.

General feeding

In nature, Telmatherina sarasinorum mainly feeds on small prey found at the surface and in the water column. Its diet includes zooplankton, small crustaceans and insects, along with various aquatic larvae. In aquaria, it accepts small dry foods, but a varied diet supports better condition and coloration. Offer fine micro-pellets or flakes, supplemented with frozen or live foods such as brine shrimp, daphnia and cyclops. Portions should remain small because uneaten food can quickly degrade nutrient-poor water. Several small feedings are preferable to one heavy meal, especially during acclimation and when keeping young fish.

Essential data

• Name of original river: Lake Matano
• Local name: Opudi
• Origin of the scientific name: The genus Telmatherina was formed from Greek roots associated with marshy or wet habitats and fish.
• Etymology of the full name: Telmatherina refers to a fish associated with wet habitats; sarasinorum honors the brothers Paul Benedict Sarasin and Fritz Sarasin, naturalists who studied Sulawesi.
• Common/vernacular names: Sarasin Rainbow; Opudi
• Family: Telmatherinidae
• Subfamily: Telmatherininae
• Name pronunciation: tell math er EYE nah - sah rah sin OR um
• Discovery: George Albert Boulenger, 1897
• Maximum adult size: About 8 cm
• Water temperature and pH: 26 to 30 °C; approximately pH 7.5 to 8.5
• Waterbody appearance and surrounding vegetation: Clear tropical lake, rocky shorelines, low organic load, tropical shoreline vegetation and localized aquatic plant growth.
• Typical tankmates: Telmatherina antoniae; Telmatherina prognatha; Telmatherina wahyui; Oryzias marmoratus; Glossogobius matanensis
• Temperament and behavior: Peaceful, active and schooling; keep in groups with calm tankmates.
• Water depth: Mainly in shallow to intermediate shoreline areas.
• Sexual dimorphism: Males are generally more colorful, with more developed fins; females are often rounder and less conspicuous.
• Bottom structure and flow: Rocky and sandy-rocky bottom, sometimes mixed with plant debris; calm to gently moving water.

For greater success

Success with Telmatherina sarasinorum depends on a mature, well-filtered aquarium kept at a stable tropical temperature. Provide open swimming space, some sheltered areas and moderate flow without excessive turbulence. Alkaline, clean and highly oxygenated water is preferable to a tank loaded with organic waste. Keep the fish in a group and avoid boisterous or oversized tankmates that may intimidate them. Because this is a very rare species endemic to Lake Matano, captive breeding and the preservation of accurately identified lines are especially valuable. Its availability is exclusive to Ton.Fish in Canada.