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Histological evaluation of the parasitic load using the model Myoxocephalus scorpius and Gymnocanthus tricuspis - Trichodina spp.
KOMENDOVÁ, Klára
The main goal of this work was the study of parasitism of a shorthorn sculpin (Myoxocephalus scorpius) and an arctic staghorn sculpin (Gymnocanthus tricuspis) parasitized by ciliates Trichodina spp. Studied samples of gill originated from fish caught in 2011 and 2012 in the central part of Svalbard mainly in the bay of Petuniabukta. In the same fish, from which samples of gill were taken, parasitic endohelminths were also identified. Histological and microscopic methods were used for quantification of the ciliates and their prevalence in the samples from individual fish was compared with number of identified helminths and with the physical condition of the host fish. One of the main aims of this work was to confirm or exclude the hypothesis that the number of the parasitic ciliates Trichodina spp. correlates with the intensity of infection with endohelminths and that in general a higher level of parasitism is also reflected by a lower physical condition of fish. Another aim of the work was to improve the theoretical knowledge and the practical skills in histological methods, which included fixation, embedding, cutting and staining of tissues, and to learn the methods of microscopic diagnostics. For the histological assessment, samples of gills from a shorthorn sculpin were used. These fish were caught using a benthic gill net or during diving and then their length, total weight, weight of gonads and weight of liver were sequentially measured. The gill samples taken during pathological dissection of fish were carefully fixed for subsequent histological examination and labelled. During dissection the parasitic endohelminths were also identified and counted. The tapeworm Diplocotyle olrikii (Cestoda: Spathebothriidea), plerocercoids Tetraphyllidae gen. sp., a intestinalfluke Podocotyle atomon (Digenea: Opecoelidae) and anisakid larvae (Nematoda: Anisakidae) were among the identified parasites. Histological dissections were made from each gill.The sections were examined by the microscopes Olympus BX51 and Olympus CX 21 with objectives 20 x and 40 x.Trichodines and endohelminths were quantified and their numbers recorded together with parameters of the host fish and their calculated condition factors. The fish condition was estimated using condition factors GSI (gonadosomatic index), LSI (hepatosomatic index) and KK (condition coefficient).To determine the correlation between the number of the individual parasites, species identity and sex of fish, an analysis of main components (PCA) in program Canoco for Windows was performed.The ordination diagram showed the positive correlation between all categories of parasites with the strongest correlation between tapeworms, flukes and nematodes. Trichodines exhibited a weak positive correlation with nematodes correlation while there was almost no correlation with flukes and tapeworms. The second statistical testing was performed by the statistical program R. Using this program condition indexes dependence on the number of parasites, species identity and sex of fish was assessed. The results did not show the negative effect of parasites on the condition of the fish, on the contrary the condition indexes of fish were increasing with increasing number of parasites. It is likely that the used indexes might not be ideal indicators of condition because they reflect mainly the size (and thus age) of fish. Different results were obtained using the condition coefficient (KK), which showed a trend towards a negative dependence on trichodina and endohelminth numbers. However, this trend was not statistically significant.
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