Harlequin rasbora

Appearance

The harlequin rasbora is a fish that has an approximately lozenge-shaped body, whose basal colour from the head to the caudal peduncle is an orange-pink, the exact hue varying depending upon such factors as water conditions and the original population from which the fish was obtained. The posterior half of the body is overlaid with a large, roughly triangular black marking, that tapers toward the terminal end of the caudal peduncle, and begins approximately below the midpoint of the attachment of the dorsal fin. In common with all cyprinids, the articulation of the pectoral and pelvic fins follows a familiar pattern, the pectoral fins being located immediately posterior to the operculum or gill cover, whilst the pelvic fins are located some way further back along the ventral portion of the body, in this case almost directly in a vertical line drawn through the dorsal fin. This relationship between the pectoral and pelvic fins is seen in characins as well as cyprinids, and is a feature of all the ostariophysans.

The dorsal, anal, caudal and pelvic fins are all tinted red, the caudal fin being forked, with the red colour concentrated in the outermost rays, the inner section of the tail fin being more hyaline.

It is possible to confuse this fish with two similar species that were indeed originally considered to be subspecies of "T. heteromorpha", namely "Trigonostigma espei" and "Trigonostigma hengeli". These fishes are more 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.

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

The harlequin rasbora is a native of Malaysia, Singapore, Sumatra and southern Thailand. It is an inhabitant of streams and other waterbodies that are located in peat swamp forests.

Habitat

The harlequin rasbora 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.

Reproduction

The harlequin rasbora differs considerably from the other popular rasboras in the aquarium with respect to breeding. Whilst other rasboras are egg-scattering spawners, the harlequin rasbora deposits adhesive eggs on the underside of the leaves of plants such as "Cryptocoryne" and "Aponogeton". The female will swim in an inverted position beneath a chosen leaf, rub her belly along the leaf in preparation for spawning, this action seemingly encouraging the male to join in spawning. When the male joins the female, he adopts a similar inverted position alongside her, and as the female extrudes her eggs and attaches them to the underside of the leaf, the male curls his tail fin around the body of the female and with a trembling motion, emits the sperm that will fertilise the eggs. Six to 12 eggs at a time are deposited in this fashion with each such embrace, and the fishes repeat this course of action over a period of two hours or more, during which a large and well-conditioned female may deposit as many as 300 eggs, though 80 to 100 is a more typical number.

The breeding aquarium for the harlequin rasbora requires the presence of suitable plants—"Cryptocoryne" species being the premier choice. The water in the breeding aquarium must be soft and acidic, as the fish are unlikely to spawn in hard, alkaline water, and furthermore egg fertility appears to be adversely affected in such conditions even if the parents do spawn. Aquarists intent upon simulating natural conditions as closely as possible may choose to filter the aquarium water over peat, thus replicating the humic acid concentrations found in the fish's native waters, though this is not absolutely necessary if the basic water chemistry parameters are correctly maintained. Temperature for breeding should be 28°C, and the parent fish should be conditioned heavily with live foods such as "Daphnia" and mosquito larvae prior to the spawning attempt. Once spawning is completed, the parent fishes should be removed from the breeding aquarium to prevent instances of egg eating, which may occur with this species.

An excellent illustration may be found in William T. Innes' book "Exotic Aquarium Fishes" on page 171, illustrating the inverted position adopted by the female during the preparation for spawning.