Harlequin Rasbora - Reproduction

Reproduction

The Harlequin Rasbora differs from the other popular "Rasboras" in the aquarium considerably 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. 6 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 2 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 fishes 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 (no higher than 4°dH hardness, pH around 6.4) are correctly maintained. Temperature for breeding should be 28°C(82.4°F), and the parent fishes 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 (black-and-white photo) 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.