Clown Rasbora (Rasbora Kalochroma)

A peat-swamp jewel wearing bold black clown markings.

Clown Rasbora (Rasbora kalochroma) is a striking softwater shoaling fish for planted blackwater aquariums, best kept in groups in acidic, gentle water.

• Species overview and natural habitat: The Clown Rasbora, Rasbora kalochroma, is a beautiful cyprinid from the blackwater streams and peat swamps of Southeast Asia, including parts of the Malay Peninsula, Sumatra and Borneo. It is prized for its warm orange-red body, bold dark blotches and peaceful shoaling behaviour. Adults can reach around 8–10 cm, making this a robust but still community-friendly rasbora for a carefully set-up softwater aquarium. In nature it lives in shaded, tannin-stained water with leaf litter, submerged roots and gentle flow, so recreating that environment is the key to keeping it colourful and relaxed.
• Water conditions: Clown Rasboras do best in soft, acidic water. Aim for a pH around 5.0–6.8, a general hardness of roughly 1–8 dGH, and a temperature of 22–26°C. They are not a good match for hard, alkaline tap water, and stability matters more than chasing an exact number. Ammonia and nitrite should always be zero, with nitrate kept low through regular maintenance and modest stocking. Tannins from driftwood, catappa leaves or other botanicals are beneficial and help mimic their natural blackwater habitat. Use a gentle filter, avoid strong surface disturbance, and acclimatise new arrivals carefully with drip acclimation, especially if the pH or hardness differs from the holding water.
• Tank setup and size: A group of Clown Rasboras needs swimming space, so choose an aquarium of at least 90 cm in length and around 120 litres, with larger tanks being better for long-term shoals. The tank should be mature, well covered and thoughtfully scaped with driftwood, dark substrate, leaf litter, floating plants and shaded planting. Dim lighting and dappled cover bring out their best colours and reduce stress. Keep the water movement gentle, provide open midwater swimming space alongside secure planted areas, and fit a tight lid because rasboras can jump when startled. A blackwater or botanical-style setup is ideal, but good filtration and stable water quality should never be sacrificed for aesthetics.
• Suitable tank mates: Clown Rasboras are peaceful shoaling fish and should be kept in a group of at least eight, preferably more. Good tank mates include other peaceful softwater species such as harlequin rasboras, espei rasboras, pencilfish, hatchetfish, kuhli loaches, dwarf chain loaches, small Corydoras catfish and peaceful dwarf cichlids suited to acidic water. Avoid large or predatory fish, aggressive barbs, fin-nippers, goldfish and livebearers that require hard, alkaline water. Very small shrimp or fry may be treated as food, so plan the community around adult fish and provide plenty of cover. A larger shoal spreads confidence, reduces shyness and encourages more natural behaviour.
• Feeding habits: Clown Rasboras are omnivorous micropredators that feed readily in midwater. Offer a varied diet based on high-quality micro pellets or finely crushed flakes, supplemented with frozen or live foods such as daphnia, brine shrimp, cyclops, bloodworm and insect larvae. Small, frequent meals are better than one large feed; give only what the shoal can clear within a few minutes, two or three times daily. A varied diet supports condition, colour and spawning behaviour, while overfeeding pollutes softwater tanks quickly. If new fish are shy, feed small amounts in the same area each day and observe that every individual gets a share.
• Care requirements: This species is sensitive to poor water quality, sudden parameter swings and high nitrate, so consistent maintenance is essential. Carry out regular partial water changes of around 20–30% weekly, rinse filter media gently in tank water, and avoid unnecessary chemical treatments. Keep the tank well oxygenated but not turbulent, maintain stable temperature, and test water regularly. Quarantine new livestock and watch for signs of stress, such as faded colour, clamped fins, heavy breathing or hiding. Because Clown Rasboras are shoaling fish, they are more secure and show better colour in a properly sized group. With soft acidic water, subdued lighting, tannins and a varied diet, Rasbora kalochroma makes a rewarding centrepiece shoal for the experienced softwater aquarist.