Ph.D. (Zoology) / D. ranarum was sampled from the Limpopo River System. It was studied morphologically by means of light microscopy of whole mounts and scanning electron microscopy. The histology of this organism was also studied. As this parasite was described in 1891, a comprehensive description of the species was done by means of scanning electron microscopy. Graphic reconstructions of the genital systems were done in order to verify and elucidate its morphology. Various areas of said systems were histologically characterised and deductions made concerning the functions of the various cell-types and structures. Two glands, i.e. a digestive- and a spermatophoric gland were identified and described from the carapace of the male. Eggs sampled in the laboratory were studied with reference to hatching times and larvae were described morphologically. It was found from the aforegoing that larvae are parasitic directly after hatching. A histological study of host-damage by the parasite was done and it was found that infestation by ranarum causes loss of epithelial tissue, oedema and haemorrhage. The shape of the lesions were correlated with the shape and orientation of the adhesive appendages of the parasite. As significant confusion exists concerning the terminology used in the study of this group of animals, a list of such terms was compiled in order to delineate this. The role of environmental temperature as a factor influencing the limited geographical distribution of D. ranarum in Africa is discussed and the theory of continental drift is proposed as a possible explanation for the global distribution of this group.

M.Sc. / At present large scale extensive cropping of fish populations of impoundments is being undertaken by the agricultural departments of the government of the Republic of Venda and selfgoverning states of Lebowa and Gazankulu. Parasitological surveys coinciding with the cropping program revealed that Clarias gariepinus (Burchell, 1822) and Oreochromis mossambicus (Peters, 1852) were infested by fish lice of the genus Dolops (Crustacea: Branchiura). A study was therefore initiated to examine the extent of these infestations and other impoundments in Transvaal were also included. A total of 14 localities in Transvaal extending from Bloemhof Dam in the Southwest to Luphephe and Nwanedzi Dams in the Northeast were surveyed during 1982 and 1983. At these localities fish were collected by means of gill nets, seining and electrofishing techniques. The collected fish were examined in a field laboratory at the collection localities for the presence of ectoparasitic Dolops. The fish were weighed and measured and the site of attachment of the parasites, if present, were recorded. The parasites were removed and fixed in either hot formalin or AFA. A number of parasites were transported alive to the laboratory in Johannesburg where they were kept in glass aquaria and their life cycle studied. A morphological description based on light microscopy as well as scanning electronmicroscopy of the eggs, larvae and adults were made, and comparative body dimensions of parasites from various localities recorded. It was found that only one species of Dolops that is D. ranarum (Stuhlmann, 1891) occurred in Transvaal. This parasite was found in only five of the 14 examined localities of which all were situated in Northern Transvaal, north of the watershed.