Harlequin Rasbora

Provide a minimum of about 60 litres for a proper school, densely planted with driftwood and some floating cover to give the dim, shaded feel they prefer, while keeping an open central area for the shoal to swim. A dark substrate and subdued lighting bring out their colour. Fit a lid, as small rasboras can jump.

Harlequins are omnivorous micro predators, so feed small flakes or micro pellets that suit their tiny mouths, plus frozen or live daphnia, baby brine shrimp and micro bloodworm. Offer a small pinch once or twice a day that they finish quickly, since overfeeding fouls the water fast with such small fish.

Keep the water at 22 to 27 degrees Celsius, soft, and slightly acidic to neutral at pH 6.0 to 7.5, reflecting their blackwater origins, though they adapt to moderate hardness. The tank must be cycled with ammonia at 0 and nitrite at 0 and nitrate low. Dechlorinate tap water, and change about 25 percent weekly with matched temperature water. Driftwood and leaf litter that release gentle tannins help recreate their natural habitat.

Harlequins are schooling fish and must be kept in a group of at least eight to ten, as a larger shoal keeps them confident, colourful and active, while a small number leaves them nervous, pale and prone to hiding. They are extremely peaceful and make an ideal centrepiece for a calm community of other small, gentle fish.

Dense planting, floating plants for shade, driftwood with tannins and a dark substrate all recreate their natural stream and let their colours glow, while an open mid water area gives the shoal room to move as one. A well planted layout also gives shy individuals confidence.