Emperor tetra

Nematobrycon palmeri

Blue-eyed males with a dark stripe and an extended central tail ray

Males have blue irises; females tend towards green. The male's central caudal ray is extended.

Adult length: Up to 4.2 cm (standard length, without the tail fin)
Water temperature: 23–27 °C
pH: 5–7.5
Hardness: 1–12 dGH

Native range: Native to the Atrato and San Juan river basins in Colombia.

Natural habitat: Slow river sections, small tributaries and backwaters.

Males compete with one another. A group still needs adequate space and shelter.

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Appearance and identification

Natural-coloured males typically show a broad, regular dark stripe and blue eye shine. Rainbow emperor tetras often have reddish-brown ground colour and irregular blue-green reflections. Eye colour depends on sex and lighting. Mature males develop longer dorsal, anal and caudal fins, including an extended central tail ray. Females have greener irises.