Abstract
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.