Paedocypris

Paedocypris progenetica holds the remarkable distinction of being the world's smallest known vertebrate, with the smallest recorded mature female measuring just 7.9 mm. Found in peat swamps on Sumatra and Bintan Island, it lives in extremely acidic, dark, tannin-saturated water. Its translucent, thread-like body requires a quiet species tank with micro live foods; it is not a beginner's fish despite its diminutive size. Keeping and breeding this species is a specialist achievement.

Water: 24–28 °C, pH 3.0–6.0, very soft blackwater (GH 0–4). Tank: 10 L minimum species tank; leaf litter, peat filtration, very gentle flow. Feeding: Omnivore — infusoria, micro worms, vinegar eels, freshly hatched baby brine shrimp. Behaviour: Peaceful, timid micro schooler; keep 10+ and avoid all larger tankmates. Compatibility: Species tank only; too tiny for any community setup.