Harlequin Rasbora

1) Where they come from (quick backstory)

Harlequin rasboras come from slow, plant-choked waters in Southeast Asia—think Malaysia, Thailand, Singapore. A lot of the places they live are stained tea-brown from leaves and wood, with gentle flow and loads of cover. That vibe (dim light, plants, calm water) is basically the cheat code for keeping them looking their best.

2) Setting up their tank

If you want them confident and out in the open, give them a decent group and a tank that isn’t bare. They’re small fish, but they act way braver when they have buddies and places to weave in and out of.

• Tank size: 10 gallons can work for a small group, but 20 long is where they start to look really natural and school nicely
• Group size: 8–12+ is the sweet spot; 6 is the bare minimum in my experience
• Temp: mid-70s to around 80°F (24–27°C)
• pH/hardness: they’re pretty flexible, but slightly acidic to neutral and on the softer side keeps them happiest
• Filter/flow: gentle to moderate; avoid blasting them with a powerhead-style current
• Layout: plants (especially mid/background), some open swimming room, and darker substrate if you want better color
• Lighting: not super bright; floating plants or tannins calm them down fast

They don’t need blackwater conditions, but they do appreciate a “soft” look—driftwood, leaf litter, floating plants. I’ve kept them in clear water too, but they colored up and schooled tighter in a slightly dim, planted setup.

3) What to feed them

Harlequins are easy eaters. They’ve got small mouths, so you’ll get better results with smaller foods rather than big flakes that they have to spit and chase.

• Staples: a quality micro pellet and/or crushed flake
• Frozen: baby brine shrimp, cyclops, daphnia, finely chopped bloodworms (as a treat)
• Live (if you can): baby brine shrimp is basically magic for color and conditioning
• Feeding rhythm: small portions once or twice a day; they’re enthusiastic and will beg like they’re starving

4) Behavior and tankmates

They’re classic peaceful schooling fish. In a good-sized group they’ll do that little “follow the leader” cruising pattern, and the males will spar without causing damage—more like showing off than fighting.

• Great tankmates: other small peaceful schooling fish, dwarf corys, otos, small loaches, peaceful gouramis, shrimp (adult shrimp usually fine)
• Also good: most community-friendly tetras if your water parameters overlap
• Skip: fin nippers (tiger barbs), big/boisterous fish, or anything that sees small fish as snacks
• With bettas: sometimes works in larger, planted tanks, but watch for chasing or stressed rasboras hiding

5) Breeding tips (if you feel like trying)

Breeding harlequins is doable, but it’s not as “easy mode” as livebearers. The fun part is their spawning behavior: they like to lay eggs on the underside of broad leaves (Crypts are the classic choice).

• Use a separate breeding tank if you actually want fry—adults will snack on eggs
• Softer, slightly acidic water helps a lot; warm temp and gentle filtration
• Add broad-leaf plants (Cryptocoryne, Anubias, or even a clean, broad artificial leaf)
• Condition with live/frozen foods for a week or two
• Dim lighting and some cover seem to encourage spawning

Fry are tiny at first. You’ll need appropriately small foods (infusoria/rotifers, then baby brine shrimp once they’re big enough). If that sounds like a hassle, enjoy them as display fish—nothing wrong with that.

6) Common problems to watch for

Most issues with harlequins aren’t exotic—they’re usually the same community-tank headaches: stress, water quality swings, and new-fish sickness.

• Faded color/hiding: tank too bright, not enough cover, group too small, or pushy tankmates
• Ich and other parasites: often shows up after adding new fish; quarantine helps a ton
• Mouth too small for food: big flakes get spit out—switch to micro pellets or crush the flake
• Wasting away/skinny fish: can be internal parasites or competition at feeding time; watch that everyone actually eats
• Sudden losses after a water change: they don’t love big parameter swings—match temp and don’t do massive changes if your tap is very different from tank water