A survey of the metazoan parasite assemblage of snoek, Thyrsites atun (Euphrasen, 1791), off South Africa with an assessment of host-parasite relationships and potential biological tags

Parasites are a ubiquitous but often unseen, unacknowledged and understudied component of biological communities. However, their roles in structuring ecosystems, their influence on the evolutionary history of host species and their potential applications are slowly being uncovered. The snoek, Thyrsites atun, is a nomadic predator native to the cold coastal waters of the southern Hemisphere. Being a major target of the South African inshore line-fishery, the snoek is a socioeconomically important species whose ecological significance in the southern Benguela should not be underestimated. This study aimed to survey the metazoan parasite community of snoek off South Africa, assess host-parasite relationships and evaluate the potential of parasites as biological tags for stock structure studies. Examination of 210 snoek (FL 411 - 1040 mm) revealed them to be host to 16 parasite taxa. These included 9 new host records (Tentacularia coryphaenae, Caligus coryphaenae, Caligus dakari, Corynosoma australe, Nothobomolochus fradei, Hatschekia conifera, Bolbosoma vasculosum, Rhadinorhynchus cadenati, Digenea sp.) and 4 new locality records (Molicola uncinatus, Pseudoterranova sp., C. dakari, B. vasculosum). A further three cosmopolitan taxa (Anisakis sp., Kudoa thyrsites, Hepatoxylon trichiuri) as well as Caligus zei were also recorded

Studies on the diversity and distribution of marine ichthyoparasites in Southern Africa

Parasites are a vital component of ecosystems. However, their contribution to the functioning and structuring of ecosystems has historically been overlooked worldwide. In South Africa, marine ichthyoparasitology has a long history but research has largely been confined to taxonomic studies and the literature pertaining to marine ichthyoparasites is highly fragmented. This situation makes it difficult to gauge advances in marine parasitology, identify knowledge gaps and hampers our understanding of their ecological roles in the marine environments of Southern Africa as well as their use as tools in fisheries science. This thesis aims to explore the diversity of metazoan marine ichthyoparasites reported from Southern African waters and to examine their inter- and intraspecific distribution in marine fishes. A review of two centuries of parasitological literature, 1818 to 2017, revealed that 378 marine ichthyoparasites have been recorded off South Africa and included taxa from six phyla: Acanthocephala (12), Annelida (6), Arthropoda (210), Cnidaria (11), Nematoda (6) and Platyhelminthes (133). The parasites formed 723 unique host-parasite pairs with 269 host taxa spread across the classes Actinopterygii (186), Elasmobranchii (80), Holocephalii (2) and Myxini (1). Host species with the most diverse parasite assemblages were species of commercial significance, namely Thyrsites atun (20) followed by Merluccius capensis (17). The dominance of arthropods and platyhelminthes, which together accounted for 90.7% of the parasites found, reflects the interest and expertise of local and foreign researchers who have worked in South Africa. The parasite assemblage of selected commercially significant fish species was used to assess the degree of interspecific similarity in parasite community structure and identify the drivers of ichthyoparasite community assembly in the Southern Benguela. The examination of 554 specimens comprising six fish species (Brama brama, Chelon richardsonii, Merluccius capensis, Merluccius paradoxus, Sardinops sagax and Thyrsites atun) caught off the South African west coast revealed that they hosted 41 metazoan parasite taxa. These included 10 new host records and five new geographic records. Thyrsites atun and C. richardsonii had the most speciose component communities being infected by 17 and 14 taxa respectively. Multivariate analyses revealed that host habitat and identity in conjunction with the host specificity of ectoparasites influenced the community structure of ectoparasitic assemblages. Larval endoparasite community structure, on the other hand, differed between inshore and offshore habitats. Within the offshore habitat, further variation in endoparasite communities were driven by the host species‘ position in the food web, its trophic ecology and its vulnerability to potential final hosts of larval parasite taxa. A survey of the metazoan parasites of snoek (Thyrsites atun) caught in the Southern Benguela (n = 262) and the Northern Benguela (n = 87) revealed 18 taxa comprising 12 new geographic records for the Northern Benguela. A generalised additive mixed model (GAMM) indicated that infracommunity richness of snoek was determined by host size. Multivariate analyses revealed an ontogenetic shift, driven by an increase in the prevalence and infection intensity of trophically transmitted taxa (Anisakis sp., Corynosoma australe, Hepatoxylon trichiuri, Molicola uncinatus), in infracommunity structure as well as in the long-lived larval parasite assemblage. A ‗Random Forest‘ analysis selected Anisakis sp. and M. uncinatus as potential biological tags for assessing the population structure of snoek in the Benguela ecosystem. GAMMs with binomial and Tweedie error distributions were used to respectively assess the prevalence and abundance of both selected taxa in relation to host traits, seasonality and region of origin. The analyses demonstrated that anisakids were more prevalent and abundant in snoek caught in the Southern Benguela while M. uncinatus were more prevalent in snoek from the Northern Benguela. The spatial differences in infection levels of both parasite taxa suggest the presence of two snoek populations in the Benguela ecosystem. The information collected, collated and presented in this thesis has enabled an assessment of the present state of marine ichthyoparasitology off Southern Africa. Although the work uncovered a diverse ichthyoparasite fauna, it also revealed a bias towards particular parasitic taxa. The study highlighted a need for wide-ranging parasite surveys not restricted to certain host or parasite taxa in order to improve our knowledge of marine ichthyoparasite diversity in South Africa. The thesis also provided the first assessment of the drivers of parasite community assembly in the Southern Benguela and demonstrated that host ecology and the characteristics of the parasites played an important role in determining their distribution and interspecific distribution. Geographic differences in snoek parasite distribution patterns which reflect ecological variations across ecosystems have also proved useful to inform fishery management

First record of the Southeast Asian walking catfish, Clarias batrachus (Pisces: Clariidae), from the island of Mauritius, south-western Indian Ocean

The presence of Southeast Asian walking catfish, Clarias batrachus, in Mauritian freshwater systems has been confirmed. Three female Clarias batrachus were caught in Rivière Sèche, close to the town of Phoenix, Mauritius (20°17′ S, 57°33′ E). This constitutes the first record of the introduction of this species into the wild on the island of Mauritius.Keywords: alien species, aquarium release, biological invasions, freshwater fishe

Ectoparasites infecting the heads and gills of commercially valuable marine fishes in South Africa

The South African marine environment is highly diverse, containing >12 000 species of flora and fauna. However, the state of knowledge of marine fish parasites in South African waters is still relatively poor. This study used opportunistic sampling to examine the heads and gills of several commercially valuable marine fish species for ectoparasites with the aim of increasing knowledge of marine parasite biodiversity in South Africa. Samples were collected in 2015 and 2016 from commercial fishing operations, local fishers and research cruises by the Department of Forestry, Fisheries and the Environment and were stored frozen until dissection. The head region, gills and opercula from altogether 621 individual fish from 16 host species were examined. In total, 22 parasite taxa, comprising seven monogeneans and 15 copepods, were recorded, with one new host record and 13 new geographic records catalogued for South Africa. This study increases the knowledge of marine parasite biodiversity in South Africa.              &nbsp

First account of the metazoan parasite fauna of oilfish Ruvettus pretiosus Cocco, 1829 (Perciformes: Gempylidae) in South African waters

Parasites are an important but neglected component of ecosystems that can be used as indicators of host biology and ecology. In the present study, the metazoan parasite assemblage of Ruvettus pretiosus, an understudied but widely distributed predatory gempylid, caught off South Africa was surveyed. A total of seven parasite taxa, including four new infection records (Bolbosoma capitatum, Rhadinorhynchus sp., Hepatoxylon trichiuri and Anisakis sp.), two new locality records (B. capitatum and Rhipidocotyle sp.) as well as the ectoparasitic copepod Sagum foliaceus and the cestode Tentacularia coryphaenae were recovered from the eight specimens examined.Keywords: Benguela, mesopelagic, parasitism, teleos