Black Ruby Barb

The black ruby barb is among the most striking small cyprinids in the genus Pethia. Outside the breeding season it looks unassuming, a beige-grey body crossed by three or four dark vertical bars, but a mature male transforms completely: his head and forebody flush a deep, almost glowing ruby-purple while the dorsal fin darkens to black. Females keep the plainer greyish colouring and a rounder body. Adults reach roughly 5.5 cm, and males stay noticeably smaller and slimmer than females. The species is endemic to Sri Lanka, restricted to the Kelani and Nilwala river basins in the island's south-western wet zone. It lives in cool, shaded forest streams at around 300 metres of elevation, where the flow is gentle and the bed is sand or gravel. Leaf litter tints these soft, slightly acidic waters. Collection for the aquarium trade pushed wild populations down far enough that the IUCN lists the species as Vulnerable; almost all fish offered today are captive-bred. This is a shoaling fish: keep at least eight, ideally ten, so males display against one another and shyness disappears. A 100-litre tank on an 80 cm footprint, densely planted over a dark substrate with open lanes for swimming, shows them at their best. They are undemanding omnivores that take flakes and granules but colour up on live or frozen daphnia, brine shrimp and bloodworm. Breeding is within reach, as they scatter eggs among fine-leaved plants, though the adults eat them and must be removed. The common mistake is keeping three or four: undersized groups turn nervous and may nip slower tankmates.