An account is given of the parasitic Copepoda and Branchiura of the fishes of Lake Nyasa.
At least thirteen species of parasitic Copepoda and four species of Branchiura are now known from the lake, four of the copepods and one of the branchiurans being described as new in the present paper. Two of the copepods have been assigned to new genera.
Of the recorded species nine copepods and two branchiurans are so far known only from L. Nyasa.
Notes on the structure, habits, host preferences, and development of several species are given, and quantitative data on the incidence of Lernaea bagri on Bagrus meridionalis are analysed. The larval stages of Afrolernaea longicollis gen. et sp. n. are described, and an account of the structure and behaviour of the larva of Chonopeltis inermis is given for the first time.
The extra-Nyasan distribution of some of the non-endemic species throws light on the possible migrations of the fishes serving as hosts and suggests former connections across the watersheds of several lake and river systems which are today isolated from one another. This information supports and supplements that already deduced from the distribution of fishes.
A species flock of parasitic copepods of the genus Lernaea exists in L. Nyasa. The relationships of the various species are obscured by the specialized and degenerate characteristics associated with the parasitic mode of life but it is possible to point out certain affinities and to correlate to some extent the divergent evolution of certain species with the adaptive radiation of certain genera of cichlid fishes.
The possible implications of the rich parasitic crustacean fauna of the lake on fish culture are briefly mentioned.