Chili Rasbora

Native to the blackwater swamps and peat forests of Borneo, Boraras brigittae is one of the smallest fish you can keep in a home aquarium. Adults max out around 2 cm, and females tend to be slightly larger and plumper than the vividly colored males.

When they're stressed or in poor conditions, they look washed out and unremarkable. Get the water right and plant the tank heavily, though, and the males turn into tiny living embers, deep red with a bold black lateral stripe that catches the light as they move through the water column.

They come from environments with extremely soft, acidic, tannin-stained water, and their care requirements reflect that origin honestly. pH in the 4.0 to 6.5 range suits them best, and hardness should be kept very low. Many keepers use RO water blended to target parameters, or add catappa leaves and driftwood to bring the chemistry into range. Room temperature often falls within their tolerance, but consistency matters more than hitting a specific number.

Feeding is where beginners sometimes struggle. Their mouths are genuinely tiny, and they need micro foods: baby brine shrimp, micro worms, daphnia, and finely crushed or purpose-made micro pellets. They'll ignore anything they can't physically fit in their mouth.

Group them in at least eight individuals, ideally more, and they'll school loosely, dart through moss and stem plants, and generally bring constant low-key movement to a nano setup. A heavily planted blackwater tank with a dark substrate absolutely transforms how they look. Browse some actual builds with these fish and you'll understand why they're so popular with the aquascape crowd.