Indonesian Lake Rainbowfish Care Guide - Aquarium Advice, Diet & Breeding

Indonesian Lake Rainbowfish, Telmatherina bonti, is a graceful, laterally compressed rainbowfish from the ancient lakes of Sulawesi. Its streamlined body is typically silvery to blue-grey, while mature males develop stronger iridescent colour and contrasting golden, yellow or dark markings on the fins and rear half of the body.

This species is an active midwater fish that spends much of its time moving through open water in loose groups. Males may display to one another and to females, extending their fins and intensifying their colours without usually causing serious injury.

Like other Telmatherina, it is adapted to the distinctive conditions of the Malili lake system. Lake Towuti contains clear, mineral-rich water, rocky margins, submerged wood and areas of aquatic vegetation, creating a very different environment from the slow, tannin-stained streams inhabited by many popular tropical aquarium fish.

The species is a specialised Sulawesi endemic and is not as commonly encountered as the better-known Celebes Rainbowfish. Its restricted natural range makes responsibly sourced, captive-bred fish especially valuable to aquarists who want to support the long-term conservation of unusual Indonesian freshwater species.

The Indonesian Lake Rainbowfish is endemic to Lake Towuti on Sulawesi, Indonesia, in Southeast Asia. It occurs in the ancient Malili Lakes system, a region noted for its exceptional number of endemic freshwater fishes.

A group should have at least a 120-litre aquarium, with a footprint of roughly 100 by 40 cm; a longer tank is preferable because these are active open-water swimmers. Use efficient filtration and maintain good oxygenation while leaving generous swimming space through the centre of the aquarium. Arrange smooth rocks, driftwood and hardy plants around the sides and rear, with open areas in front. A fine gravel or sand substrate is suitable, and a secure lid is advisable because active rainbowfish can jump.

Males can reach about 8 cm (3.1 inches) in total length, while females are usually smaller at around 6–7 cm (2.4–2.8 inches).

They are opportunistic omnivores with a preference for small aquatic invertebrates and other tiny organisms. Offer a varied diet of high-quality small pellets or flakes supplemented with live or frozen foods such as baby brine shrimp, daphnia, cyclops and finely chopped bloodworm. Small, regular meals are preferable, and occasional vegetable-based foods can add useful variety.

Indonesian Lake Rainbowfish are generally peaceful and work well with other similarly sized, active freshwater fish that appreciate warm, alkaline conditions. Suitable companions can include other peaceful Telmatherina, larger peaceful rainbowfish, hardy rasboras and non-aggressive gobies or small livebearers, provided the aquarium is spacious enough. Avoid fin-nipping barbs, boisterous cichlids, very slow or delicate fish, and species that require cool or distinctly acidic water. Keeping them in a proper group helps reduce nervousness and limits excessive attention being directed towards individual tankmates.

Indonesian Lake Rainbowfish are egg scatterers that can be bred by placing a mature group in a separate, well-filtered aquarium with spawning mops or fine-leaved plants. The female deposits small adhesive eggs among the fibres, where they are fertilised by the male. Remove the spawning material or transfer the eggs to a rearing container, as adults may eat them. Hatching usually takes around one to two weeks, and the tiny fry initially need infusoria or another suitably fine first food before progressing to baby brine shrimp.

Males are generally larger and more vividly coloured, with stronger iridescence, more pronounced dark or golden fin markings and fuller fins. Females are smaller, slimmer and usually more subdued silver-grey in appearance.