Gnathiids, leeches and blood protozoans of marine fishes: morphological, pathological, developmental and molecular approaches

Hayes, Polly May (2007) Gnathiids, leeches and blood protozoans of marine fishes: morphological, pathological, developmental and molecular approaches. (PhD thesis), Kingston University, .


Haematophagous, metazoan ectoparasites and protozoan blood parasites of intertidal fishes from Wales and South Africa formed the main focus of this study. The ectoparasites examined were largely juvenile isopods of the genus Gnathia, and specimens.of the leech, Zeylanicobdella arugamensis. These taxonomically distinct ectoparasites were suspected vectors of the blood protozoans, and the latter were mostly apicomplexans of the genus Haemogregarina and euglenozoans of the genus Trypanosoma. Knowledge of digestive tract anatomy in juvenile gnathiids is essential for assessing their role as potential vectors and this system was examined using histological, microscopical and computer-based techniques. Features that had been unreported, or insufficiently recorded, previously included several structures within the dorsal and ventral stomach chambers, a typhlosole-like formation in the anterior hindgut, haemozoin-like deposits in the digestive caeca of Gnathia africana and Gnathia pantherina, and an extensive gut flora. Connections between the stomach, anterior hindgut and digestive caeca were identified, salivary gland ducts were followed towards the mouthparts, and the digestive cycles of Gnathia maxillaris and G. africana juveniles were examined over a period of 30 days. The pathology associated with the attachment sites of G. africana and Gnathia sp A to teleosts, and with G. pantherina to an elasmobranch, was found to be considerable in the case of G. pantherina, while Gnathia sp A prompted the death of its host under experimental conditions. Oocyst stages, presumed to be those of Haemogregarina bigemina, were located in sections through the digestive caeca of G. africana, confirming the vector status of the isopod. Development stages of a new species, Haemogregarina curvata, were observed in the leech, Z. arugamensis, and within peripheral blood smears from several The life cycle oftrypanosomes found in Z. arugamensisand in fishes was also established, although interpreting the morphometries of these flagellates was challenging speciation proved difficult. Identical molecular sequences oftrypanosomes werefrom separate leech samples and these were close to published sequences for fish trypanosomes. Thus, both gnathiids and leeches were likely vectors of the fish protozoans. Finally, probable dual transmission of a haemogregarine and somes by a leech was illustrated, a rare event, reported infrequently in the literature.

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