slender in body shape than T. heteromorpha, and the black marking, instead of being approximately triangular, has a horizontal stripe which tapers towards the caudal peduncle, and is greatly thickened and extended downwards below the dorsal fin. Due to this fishes with this marking are commonly known as "lamb chop rasboras" due to its perceived resemblance to the butchery cut known as a lamb chop. A fully mature individual harlequin rasbora attains a standard length of two inches (5 cm). Males are cited as possessing a slightly larger black body patch than females, with the section adjoining the anal fin being more rounded in males. Ripe females are noticeably fuller in body outline. Distribution and habitat The harlequin rasbora is a native of Malaysia, Singapore, Sumatra and southern Thailand. It inhabits streams and other watercourses characterised principally by low mineral content, high concentrations of dissolved humic acids, a consequence of those waters flowing through peat swamp forests. The waterlogged soils of these forests inhibit the complete decay of leaf litter, and result in the formation of peat, which leaches humic acids and related compounds into the watercourses flowing through these forests. The conditions thus resemble those found on a different continent, namely the blackwater habitats of South America, and the water chemistry of the Asian habitats of the harlequin rasbora is accordingly similar to that of the Rio Negro. Aquarium maintenance Despite the relatively uniform water chemistry of its various habitats, the harlequin rasbora is an adaptable fish in the aquarium, provided that migration of the fishes to waters of differing chemical parameters is conducted with due care. The fish will live in an aquarium in waters ranging from a pH of 6.0 to 7.8, and hardness ranges from zero to 15°dH. However, while for maintenance purposes water chemistry is not critical provided that cleanliness of the aquarium is maintained, for breeding purposes the water chemistry becomes considerably more so (see below). The temperature range of the harlequin rasbora is usually cited as 22 °C to 27 °C (72 °F to 81 °F) (for example, Walker, 1971, p. 101) but the fish is capable of living in temperatures from 21 °C to 28 °C, and indeed usually breeds at around 28 °C (82.4 °F). The harlequin rasbora is a shoaling fish, and should be kept in a group comprising a minimum of six individuals, though shoals of larger numbers are