Harlequin rasbora of a harlequin. 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 (commonly called a "black wedge"). In common with all cyprinids, the articulation of
Operculum (fish) the shape is visible and then the individual components are developed days later. The size and shape of the operculum bone is dependent on the organism's location. For example, fresh water threespine sticklebacks form a less dense and smaller opercular series in relation to marine threespine sticklebacks. The marine threespine stickleback exhibits a larger and thicker opercular series. This provides evidence that there was an evolutionary change in the operculum bone. The thicker and more dense bone may have been favored due to selective pressures exerted from the threespine stickleback's environment. The development of the operculuar series has changed dramatically