The 'black ruby barb' ('Pethia nigrofasciata', formerly 'Puntius nigrofasciatus') or 'purple head barb' is a tropical cyprinid fish endemic to Sri Lanka, where it occurs in forested streams from the 'Kelani' basin to the 'Nilwala' basin. They are found in streams on hills around 1000 ft (300 m) in elevation. The brightly colored population introduced to 'Mahaweli' at 'Ginigathena', Sri Lanka, is said to have diminished in number due to the aquarium export trade.

The young fish has a yellowish gray body with black vertical stripes. The silver body turns into a dark ruby red color in mature, breeding males. In the female, the basal part of all the vertical fins is black. In the male, the whole dorsal fin is a deep black, the anal fin blackish red, and the pelvic fins are reddish. The fish will grow to a maximum length of 2–3 inches (6–8 centimeters) with the female being slightly longer than the male.

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