An Example of ‘Mimicry’ in Fishes

Abstract

Among the genera of Cichlid fishes peculiar to Lake Nyasa, Corematodus, comprising two species, is characterized by the dentition, which consists in each jaw of a broad file-like band of small pointed teeth. Otherwise these two species would be included in the large genus Haplochromis, of which more than a hundred, nearly all endemic, have been recorded from Nyasa. Among the Haplochromis and their related genera in Nyasa, many species have a colour pattern characteristic of the Lake and rarely met with elsewhere in Africa, namely, a dark oblique band from nape to caudal fin. Corematodus tæiatus Trewavas also has this pattern on a silver-grey ground; the largest specimen known is 19 cm. in total length. C. shiranus Blgr. has quite a different pattern, consisting of vertical, or nearly vertical, black bars extending from the back to near the ventral surface. This pattern is exactly similar to that of females and non-breeding males of the Nyasa species of Tilapia of the T. squamipinnis group; and C. shiranus reaches a length of 27 cm., which is one of the commonest lengths of the T. squamipinnis caught during the Fishery Survey of 1939¹.