Myxosporean parasites (Myxozoa: Myxosporea) infecting fishes in the Okavango River system, Botswana

Abstract

English: The Class Myxosporea Butschli, 1882 comprises an enormous group of spore forming obligatory parasites that are able to infect any organ of the hosts in which they are found. Myxosporeans mostly parasitise fish and to date there are more than 1300 species known from fishes throughout the world. In Africa, approximately 84 species have been described from primarily freshwater fish. Research on myxosporeans in southern Africa is very limited, with only a few publications appearing from the coast of South Africa during the early 20th century. In Botswana no research has ever been conducted on myxosporean parasites infecting fishes. Botswana contains one of the worlds largest inland delta systems formed by the Okavango River, which flows in a southeasterly direction from Angola. Knowledge on the fishes as well as their parasites is essential for the well being of a unique body of water such as this. Since myxosporean parasites of fish hold the potential to be pathogenic to their hosts and have been known to cause serious economical losses in aquaculture industries throughout the world, it is thus essential to determine the distribution and biodiversity of these parasites in the Okavango River and Delta in Botswana. The main aims of this project were to investigate the available literature regarding African myxosporeans, compile a database of species infecting freshwater fishes in Africa and to investigate the taxonomic status, species biodiversity and prevalence of myxosporeans infecting fishes in the Okavango River and Delta in Botswana. Fieldwork for this project was conducted in June and July 1998 and 1999 in the Okavango and a total of 275 fishes belonging to 31 species from nine different families were examined for the presence of myxosporean parasites. Five myxosporeans from the genus Henneguya Thélohan, 1892 were collected from four different fish hosts. Only one of these was identified as a known species and was described in this dissertation. A comprehensive morphological description of the four unknown species was also provided. Eight myxosporeans from the genus Myxobolus Butschli, 1882 were also found infecting nine different fish hosts, of which four were identified as known species and described. Detailed descriptions of the four unknown species were provided. It was also found that some fish species showed very high gill infections of these parasites, which may cause some form of respiratory deficiency. This current investigation into myxosporean parasites infecting fishes in the Okavango River System in Botswana provided new insight into the distribution of myxosporeans in southern Africa and has also opened the door for future research in this unique group.

Afrikaans: Die Klas Myxosporea Butschli, 1882 bestaan uit 'n groot groep verpligte spoorvormende parasiete, wat in staat is om enige orgaan van die gasheer waarin hul voorkom te infekteer. Miksosporidiums is meestal parasiete van visse en tot op hede is daar meer as 1300 spesies vanaf visse regoor die wêreld beskryf. Ongeveer 84 spesies is in Afrika beskryf, vanaf hoofsaaklik van varswater visse. Navorsing op verteenwoordigers van die miksosporidiums in suidelike Afrika is baie beperk, met slegs enkele publikasies gedurende die vroeë 20ste eeu vanuit Suid-Afrika. Geen navorsing is egter in Botswana op miksoporidium parasiete van visse gedoen nie. Botswana het een van die grootste binnelandse deltas, wat deur die suid-oos vloeiende Okavangorivier gevorm word. Die rivier het sy oorsprong in die hooglande van Angola. Kennis van die visse sowel as hul parasiete is noodsaaklik vir die ekologiese welstand van hierdie unieke stelsel. Miksosporidium parasiete is potensiële patogene en daarvoor bekend dat hulle groot ekonomiese verlieste in visakwakultuur reg oor die wêreld kan veroorsaak. Dit is dus noodsaaklik om die verspreiding en biodiversiteit van hierdie parasiete te bepaal. Die hoof doelwitte van hierdie studie was om die beskikbare literatuur rakende miksosporidiums in Afrika te bestudeer, 'n data basis op te stel van die spesies wat varswater visse in Afrika infekteer, asook om die taksonomiese status, spesie biodiversiteit en besmettings statistiek van mikspsporidiums van visspesies in die Okavangorivier en- delta te bepaal. Veldwerk vir hierdie studie was gedurende Junie en Julie 1998 en 1999 in die Okavango uitgevoer. 'n Totaal van 275 visse wat tot 31 verskillende spesies en nege families behoort was vir die aanwesigheid van miksosporidium parasiete ondersoek. Vyf spesies van die genus Henneguya Thélohan, 1892 was van vier veskillende visgashere versamel. Slegs een is as 'n bekende spesie geïdentifiseer en beskryf 'n Breedvoerige morfologiese beskrywing van die ander vier spesies is gedoen. Agt miksosporidiums van die genus Myxobolus Butschli, 1882 was van nege veskillende visgashere versamel. Vier van hierdie spesies was bekend en is beskryf, 'n omvattende beskrywing van die vier onbekende spesies is gedoen. Daar is ook gevind dat van die visspesies 'n baie hoë kieuinfeksie gehad het, wat moontlik tot respiratoriese disfunksie kan lei. Hierdie studie rakende die miksosporidium parasiete, wat visse van die Okavangorivierstelsel in Botswana infekteer, werp nuwe lig op die verspreiding van miksosporidiums in suidelike Afrika en open deure vir toekomstige navorsing op hierdie unieke groep organismes.