Branchial monogenean parasites (Monogenea: Dactylogyridae) of characin fishes from the Okavango river and Delta, Botswana

[摘要] English: The fishes of the Okavango System, Botswana, are of considerable economical andecological importance. Recently, scientists and local fishermen have reported adramatic decline in the fish stocks of the Okavango River and Delta. There are manyreasons for this decline to which fish parasites ~may at least be a contributing factor. Inrecent surveys to the Okavango, monogeneans have been found to be of the mostprominent parasites infesting the Okavango fishes. The tigerfish, Hydrocynus vittatusCastelnau 1861, especially, show high infestations of the branchial monogeneans,Annulotrema pikei (Price, Peebles & Bamford 1969).The genera Annulotrema Paperna & Thurston 1969 and Characidotrema Paperna &Thurston 1968, are exclusively parasites of characiform fish in Africa. In the Okavangothe characiforms are represented by five species, Brycinus lateralis ( Boulenger 1900),Hepsetus odoe (Bloch 1794), Hydrocynus vittatus, Mieralestes acutidens (Peters 1852)en Rhabdalestes maunensis (Fowler 1935), all of which, are infested by species of thegenus Annulotrema and only one, Brycinus lateralis (Boulenger 1900), is infested by aspecies of the genus Charcidotrema.During two field trips to the Okavango System, five Annulotrema species werecollected; three of which are known species and two new species. This is the firstrecord of monogeneans from Botswana and represents the southern most distributionrecorded of A. curvipenis Paperna 1969 & A. hepseti Paperna & Thurston 1969.Comparative descriptions of the three known species are given and the two new speciesare described as A. micralesti sp. n. and A. rhabdalesti sp. n. Mixed infestations of A.curvipenis and Characidotrema nursei Ergens 1973 were also recorded from the gills ofBrycinus lateralis. This also represents the southernmost, recorded distribution of C.nursei.Investigation of histological sections revealed that although these monogeneansoccurred in relatively high numbers on the gills of the fish, the pathology they causedwas limited. Examination of the infestation statistics showed that these parasites exhibitsite preferences to the gills on which they occurred. This preference is influenced by the number of monogeneans of the same or other species as well as the number of otherparasites occurring on the gills of the fish hosts.When considering the results, these monogenean parasites do not seem to cause severeharm to the host fish. Any changes in the environment could alter the face of thisparasite-host relationship dramatically and hence the potential pathogenicity of theseparasites should, however, not be ignored.

[发布机构] University of the Free State