The biology of gnathiid isopod parasites and their role as vectors of fish blood parasites in South Africa

Abstract

English: Research on marine fish parasites has been largely neglected in South Africa. This is especially true for the temporary fish parasites of the isopod family Gnathiidae and fish blood parasites of the family Haemogregarinidae. In this study, surveys were carried out to determine the presence of gnathiid isopods and fish haemogregarines associated with different intertidal and sub-tidal fish hosts over a period of four years, at two different localities on the South African south coast. The study also focussed on the relationship between gnathiids and haemogregarines, specifically the possibility that the gnathiid Gnathia africana Barnard, 1914 might be a vector of the fish blood parasite Haemogregarina bigemina Laveran and Mesnil, 1901. Laboratory work was conducted to elucidate the life cycle of G. cfricana. It was found that G. cfricana has three larval stages, consisting of three unfed (zuphea) and three fed (praniza) stages, with the final stage praniza larvae moulting into either male or female adults. Forty days after their last feed as praniza 3 larvae, mature females release stage 1 zuphea larvae. Detailed information was also supplied on the feeding and digestion length for each larval stage. The females of G. africana were re-described from the material collected. Furthermore, other gnathiid larvae, not resembling any of the known species from South Africa, were collected from three species of elasmobranchs as well as the evileye pufferfish. Both groups of larvae were kept in the laboratory, where they moulted into adult males that did not conform to the description of any other gnathiid species in South Africa, or worldwide. These specimens were described as new species (Gnathia pantherinum sp. n. and G. pipindae sp. n.), using light and scanning electron microscope observations. Extensive information was also provided on the final life cycle stages of G panthertnum sp. n. Special attention was given to finding distinguishing characteristics to identify females and larvae of various species in the absence of males. Comparing material in this study with information from the literature showed that the morphology of the pleotelson and cephalosome appendages of females and larvae could be successfully used as differentiating characteristics. The research conducted on fish haemogregarines led to new distribution and host records for two known species, and the description of two new, but un-named species. Development stages of H. bigemina were found in the gut of G. africana larvae that had fed on H. bigemina-infected host fish. The data obtained from these results was used to compile a complete life cycle for H. bigemina in both the fish and the arthropod host.

Afrikaans: Navorsing op mariene visparasiete in Suid Afrika is grootliks nagelaat. Dit is veral waar vir die tydelike visparasiete van die isopood familie Gnathiidae en die visbloedparasiete van die familie Haemogregarinidae. Die teenwoordigheid van isopode van die genus Gnathia en vishaemogregarienes, was oor 'n periode van vier jaar by twee verskillende lokaliteite aan die Suid-Afrikaanse suidkus ondersoek. Hierdie studie fokus ook op die interaksie tussen verteenwoordigers van die genus Gnathia en haemogregarienes, en spesifiek die moontlikheid dat die isopood, Gnathia africana Barnard, 1914 as vektor van die haemogregarien, Haemogregarina bigemina, Laveran and Mesnil, 1901 kan optree. Laboratoriumeksperimente was op die lewenssiklus van G. africana onderneem. Daar was bevind dat die lewenssiklus van G. africana uit drie verskillende larwaalfases bestaan. Die finale praniza 3 larf vervel in 'n volwasse mannetjie of wyfie. Wyfies gee geboorte aan fase 1 larwes, 40 dae nadat sy as praniza 3 larf die visgasheer verlaat het. Gedetailleerde inligting oor die voeding en vertering van elke larwaalfase word ook verskaf. Die wyfies van G. africana word hierin vanaf die versamelde materiaal herbeskryf. Isopood larwes, wat nie aan die beskrywings van die larwes van enige bekende Suidelike-Afrika spesies voldoen het nie, is vanaf drie kraakbeenvisspesies en die groenoogblaasop versamel. Beide hierdie groepe larwes is in die laboratorium aangehou waar hulle na volwasse mannetjies vervel het. Hierdie mannetjies het nie dieselfde einskappe as enige ander beskryfde spesie in Suid Afrika of die res van die wêreld besit nie en is gevolglik as nuwe spesies, G. pantherinum sp. n. en G. pipinde sp. n. beskryf. Die spesiebeskrywing is op lig-en skandeer-elektronemikroskoop waarnemings gebaseer. Uitgebreide inligting oor die finale lewenssiklusstadiums van G. pantherinum is ook verskaf. Spesiale aandag is aan die ondersoek na morfologiese kenmerke om wyfies en larwes van verskillende spesies in die afwesigheid van mannetjies te identifiseer, geskenk. Die materiaal gedurende hierdie studie versamel, sowel as informasie uit literatuur, is vergelyk en daar is gevind dat die morfologie van die pleotelson en die kefalosoomaahangsels suksesvol as onderskeidende kenmerke gebruik kan word. Die navorsing op vishaemogregarines het tot nuwe verspreidings- en gasheerrekords van twee bekende spesies gelei, sowel as die beskrywing van twee nuwe spesies. Verskillende ontwikkelingstadiums van H. bigemina was in die maag van G. africana larwes, wat op H. bigemina geïnfekteerde visse gevoed het, gevind. Die data van bogenoemde resultate was gebruik om 'n volledige lewenssiklus van H. bigemina vanuit beide die vis-en arthropopdgashere saam te stel.