Bleeding-heart tetra

The bleeding heart tetra is native to the sluggish, tannin-stained tributaries and forest lakes of the upper Amazon where Brazil, Peru and Colombia meet. The striking red blotch on the flank — the "bleeding heart" — is unique among characins and gives the fish its common name. Adult males grow to about 6 cm and develop noticeably extended dorsal, pelvic and anal fins, while females stay rounder and slightly smaller.

These tetras need soft, acidic water to thrive. In the aquarium keep the temperature at 21–28 °C and pH at 4.0–7.5, though they colour up best at the softer, more acidic end of that range. Dimly lit tanks with a dark substrate, floating plants and leaf litter that leaches tannins suit them well. A tank with a footprint of at least 90 × 30 cm (about 81 litres) is recommended for a mixed-sex group of eight to ten. They are intolerant of accumulated organic waste and must never be added to an uncycled tank.

In the wild the stomach contents of specimens from Lake Ayapuá were over 98 % fruit remains, with the rest being aquatic insects. In captivity they accept good-quality flakes and granules but need regular live or frozen foods — bloodworm, Daphnia and Artemia — to maintain condition. Submerged pieces of fresh fruit are also eagerly grazed.

Despite the territorial displays that males perform towards one another, this is a peaceful species that fits well in a community of similarly-sized characins, corydoras and small cichlids. It is an egg-scatterer with no parental care. The species is known to be susceptible to a condition that makes the scales appear metallic gold; affected fish show no discomfort and their lifespan appears unaffected.