Biodiversity and systematics of branchial cavity inhabiting fish parasitic isopods (Cymothoidae) from sub-Sahara Africa
Van der Wal, Serita
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Isopods from the family Cymothoidae Leach, 1814 are well known ectoparasites of marine and freshwater fishes, most often attaching to the external surface, branchial chamber or buccal cavity of their hosts. Cymothoids have a cosmopolitan distribution but are mostly recorded in warmer, tropical regions from shallow, coastal waters, to the deep sea. The sub-Sahara African coastal region complies with these characteristics that favour the establishment of cymothoids as many species have already been recorded from this region. Within the Cymothoidae family, the branchial attaching genera Norileca Bruce, 1990; Elthusa Schioedte & Meinert, 1884 and Mothocya Costa, in Hope, 1851 have been recorded from the sub-Sahara African region. Although it is expected that the biodiversity of these cymothoids would be much higher in this region than what is currently recorded, there are many challenges that obstruct the advancement of the taxonomy of these cymothoids. These challenges have hindered the research of cymothoids in many regions, leaving numerous species undiscovered or undescribed. This observation has led to the hypothesis that it is the lack of sampling and collection, rather than the lack of species, that accounts for the low number of branchial cavity attaching cymothoid species from the sub-Sahara African region. To test this hypothesis, unexamined specimens from sub-Sahara Africa were collected and examined, including museum material. These sample specimens were subjected to morphological analysis to provide full descriptions of each identified species, and to confirm the taxonomic placement of unidentified museum material. Molecular characterisation on fresh material was done by sequencing a fragment of the mitochondrial cytochrome oxidase I (COI) gene, providing genetic data and confirming morphological analysis. Diagnostic identification criteria have been provided, along with identification keys, to simplify and aid in the correct identification of species in future collections. The genus Norileca contains three known species, of which only one species, Norileca indica (Milne Edwards, 1840), has been recoded from sub-Sahara Africa. Norileca indica is fully redescribed based on ovigerous females collected from Maputo Bay, Mozambique, from the branchial cavity of the fish host Selar crumenophthalmus Bloch, 1793. The first comprehensive description of a male specimen is also included and an identification key to the species of Norileca Bruce, 1990 is given. Furthermore, a fragment of the mitochondrial cytochrome oxidase I (COI) gene from N. indica was sequenced for the first time. This is the first molecular characterisation of a species of Norileca. Elthusa is considered to be among the most morphologically varied and species-rich genera of the family Cymothoidae, consisting of 31 described species. Elthusa raynaudii Schioedte and Meinert, 1884 is the only species that has been recorded from sub-Sahara Africa, and from southern Africa in particular. Three distinct species of Elthusa have been identified in the current study, E. raynaudii as well as two undescribed species. Specimens obtained from RV Africana and those collected from Alexander Bay during 1993 represent new species. In addition to the morphological analysis, each identified species was sequenced using a targeted part of the mitochondrial cytochrome oxidase I (COI) gene. These sequences were used to confirm the distinction between the species as well as to determine their phylogenetic placement and relationship to other genera from the family Cymothoidae. The genus Mothocya contains 31 globally distributed species. Specimens resembling Mothocya were examined. This material originated from sub-Sahara African countries Nigeria and Kenya. From morphological analyses, three Mothocya species could be identified. These included one well-known and described species, Mothocya renardi (Bleeker, 1857) collected from Kenya. The remaining two species, both from Nigeria, resemble new and undescribed species. Full descriptions and diagnostic information were provided for these new species. In addition to the description of four new branchial cavity attaching species, a case study was done on the effects that these ectoparasites might have on their hosts. For this case study, Mothocya affinis Hadfield, Bruce & Smit, 2015 and its host, the tropical halfbeak Hyporamphus affinis (Günther, 1866) were collected from Sodwana Bay, South Africa. By considering the relatively large size and attachment techniques of these parasitic cymothoids to their hosts, it was expected that they would induce some measure of negative impact on the fish host‘s health. This led to the second hypothesis, that branchial cavity inhabiting cymothoids would have a quantifiable or noticeable negative impact on the health of its host. In order to test this second hypothesis, the case study was executed to determine the visible effects and change in health condition of infected hosts compared to uninfected fish. A fish health assessment yielded no significant difference in the condition and health of infected hosts, compared to uninfected ones. Although condition indices provided no substantial evidence of internal health effects, the physical effects of these branchial attaching cymothoids were evident, especially at the site of attachment. Thus, both hypotheses were confirmed. An increase in sampling and collection of cymothoids across sub-Sahara Africa yielded four new species from two branchial cavity inhabiting cymothoid genera. In addition, the genetic data of all species encountered was obtained. Frayed and discoloured gills, shortened opercula, and a physical depression created by the attachment of the gill parasite were noticed. This provides evidence that branchial cavity attaching cymothoid genera can have a negative effect on the general health of their fish hosts.