World's Smallest Fish (Paedocypris progenetica)

Paedocypris progenetica holds the scientific record as the world's smallest known vertebrate, reaching a maximum length of just 10 mm. Native to the highly acidic peat swamp forests of Sumatra where the water is so tannin-rich it resembles black tea, its almost transparent body is virtually invisible in planted nano aquariums. Feeding must consist of the tiniest live foods — micro-worms, infusoria, and copepods — making this a specialist species for the most dedicated nano aquarists.

Species-only nano tank of at least 20 L with ultra-soft, ultra-acidic blackwater: pH 3.0–4.5, GH 0–2, KH 0–1, temp 24–28°C. Use RO water conditioned with peat or catappa leaves only. Feed exclusively micro-sized live foods: vinegar eels, micro-worms, infusoria, and baby brine shrimp nauplii. Zero tolerance for elevated hardness or alkalinity. Extremely fragile — handle only with specialist experience. A conservation curiosity rather than a community fish.