Jewel tetra

The serpae tetra reaches about 4 cm standard length and is sold under a pile of other names, among them jewel, red minor, blood and callistus tetra, along with selectively bred metallic, long-finned, balloon and fairy-fin strains. Its natural range is enormous, covering much of the Amazon drainage in Brazil, Peru and Bolivia plus the Río Paraguay in Brazil, Paraguay and Argentina, and the aquarium trade has since introduced it to French Guiana. Wild populations differ in fin colour and in the size and shape of the shoulder spot, and some were once described as separate species; those names may yet be restored.

In the wild it holds to still and sluggish tributaries, backwaters, ponds and small lakes, forming loose aggregations around marginal plants and submerged tree roots. A tank of 80 by 30 cm, roughly 72 litres, is the minimum for a group of this species without other upper-water fish; a community requires more space. Colour comes out best over a dark substrate in a well-planted setup with wood and shady corners, and dried leaf litter is worth adding: as it breaks down it seeds microbe colonies that feed fry and releases tannins that mimic the natural water.

Water of 20 to 28 °C, pH 5.0 to 7.5 and 1 to 15 dGH covers this species. Nearly all fish on sale are commercially bred and take that whole range comfortably; wild stock does better kept slightly acidic to neutral. Temperament is the thing to plan around. This territorial species nips the fins of slow or long-finned tankmates, so keep a dozen or more to spread the aggression inside the group and pick brisk, short-finned neighbours. Feed good flake alongside live and frozen bloodworm, daphnia and brine shrimp. Not suitable for shrimp tanks.