D.Phil. / Branchiuran crustaceans are fairly common parasites of freshwater fishes in Africa and are presently represented by not more than 200 described species belonging to four genera, namely: Argulus Miiller,1785; Dolops Audouin,1837; Chonopeltis Thiele,1900; and Dipteropeltis Calman,1912. Chonopeltis is, however, the only one of these genera which is endemic to Africa and species of this genus have been reported from a number of different freshwater fish hosts and localities throughout the Ethiopic region. Although 13 species of Chonopeltis have hitherto been described, lack of morphological detail and morphometric data in taxonomic and subsequent descriptions, has led to confusion and much controversy as to, for instance, the phylogenetic origin, identity and function of various structures. Consequently, the validity of the taxonomic identity or status and affinities of the various species are questionable. Lack of important morphological information has also caused a considerable number of gaps and deficiencies in our present understanding of various aspects of ecological and pathogenetic significance. In the present study, a comprehensive investigation on various aspects of the morphology, anatomy and histology of adult Chonopeltis specimens was conducted, using not only light microscopy, but also scanning electron microscopy (SEM), histological microtomizing and staining techniques and graphic reconstruction. This investigation is based on several specimens of Chonopeltis victori Avenant-Oldewage,1991 collected during surveys of freshwater fish parasites in 1990 and 1991 from four different fish hosts, namely: Labeo rosae S teindachner,1894; L. congoro Peters, 1852; L. ruddi Boulenger,1907 ; and Barbus marequensis A. Smith,1841, sampled at various localities in the Olifants River in the Kruger National Park, as well as several C. australis Boxshal1,1976 specimens found on L. capensis (A. Smith,1841) and L. umbratus (A. Smith,1841), sampled in Boskop Dam near Potchefstroom. By making use of the mentioned methods of investigation a more complete and reliable morphological description of the distinctive external structures, as well as the internal structures of the cephalic shield alae and especially the reproductive system of these parasites could be given. With the aid of semi-thin (2am) serial sections and graphic reconstruction the various components of the reproductive systems could clearly be identified and the mutual relations and histomorphology of these components be described, discussed and compared with those of other members of the Branchiura. In an attempt to determine the true taxonomic position and relationships of the recognised species of Chonopeltis, the original descriptions, morphometric data, geographical distribution, hosts and affinities are compared, summarised and discussed. The results of the present study reveal a horseshoe-shaped furrow dorsally that separates the alae from the cephalon. Ventrally the frontal ala contains two marginal chitinous grooves and four sclerotized ridges which support the frontal ala. Two pairs of dorso-ventrally orientated muscles account for the movements of the frontal ala, whilst the movements of each lateral ala are controlled by a pair of transverse muscles and some longitudinal muscles. The lateral alae appear to represent the fused pleurae of the cephalic segments. The male reproductive tract consists of paired testes, vasa efferentia, vasa deferentia, ejaculatory ducts and prostate complex as well as a single median seminal vesicle and a genital atrium. Several prominent secondary sexual structures occur on the four pairs of thoracopods. The mechanism of sperm transfer presumably involves a process during which the two female spermathecal spines, being inserted into the male genital atrium, penetrate the walls of the respective ejaculatory ducts whereafter semen is actively pumped into the spermathecal vesicles. The female reproductive tract consists of a single large ovary, two anteriorly fused oviducts of which only one is functional, a genital atrium, a single median genital aperture and a crescent-shaped fertilization chamber. The paired spermathecae, each consisting of a spermathecal vesicle, duct and spine, is located separately in the abdomen and are of considerable significance during sperm transfer from the male as well as during oviposition when stored semen is presumably injected into the yet uninseminated ova. Finally, aspects on the ecology of C. victori concerning the reproductive cycle, life cycle, and epidemiology are investigated, compared and discussed.

M.Sc. (Zoology) / Please refer to full text to view abstract