| Abstract |
Epitheliocystis is a fish disease characterized by cysts formed in the gills and skin epithelium containing intracellular bacteria. The study of the disease is challenging due to its particular characteristics. The distribution of the disease is global and has been recorded in more than 90 marine and fresh water fish species, wild or cultured. There is great diversity among the bacteria causing the disease since chlamydia, β- and γ-proteobacteria have been identified so far as pathogens. In addition, these pathogens are intracellular bacteria and as a result their isolation has not been accomplished yet.
In Greece, there is an increasing trend of epitheliocystis the past few years affecting fish-farming industry in general while, particularly gilthead sea bream appears to be the most susceptible species. As causative agents of the disease have been identified Ca. Ichthyocystis sparus and Ca. Ichthyocystis hellenicum (β-proteobacteria) and bacteria of the genus Ca. Similichlamydia and Ca. Piscichlamydia as well, in gilthead sea bream, whereas, Ca. Endozoicomonas cretensis (γ-proteobacteria) has been identified in sharpsnout seabream.
The purpose of this thesis is to perform a global research on epitheliocystis in a wide range of regions in Greece in order to collect data related to the causative agents of the disease and their characteristics. Therefore, infected fish gills were collected from farmed fish and specifically, 21 gilthead sea bream, 3 European sea bass and 9 greater amberjack from 9 different regions. Molecular identification of the causative agents, phylogenetic analysis, analysis of the pathology caused and the morphometry of the cysts and observation of the bacteria were performed.
According to the results, bacteria of the genus Ca. Ichthyocystis spp. are the dominant pathogens since they were identified in all samples. Apart from the already known Ca. Ichthyocystis sparus and Ca. Ichthyocystis hellenicum that were identified in gilthead sea bream, it seems that there is a novel species that was identified in European sea bass and greater amberjack. Mainly chlamydia, or even Ca. Endozoicomonas spp. are often, also present as secondary coinfections of the gills in gilthead sea bream and European sea bass or only in gilthead sea bream, respectively. The typical pathology observed on the gill tissue is hyperplasia of the epithelium and inflammation. The cysts were categorized in 4 types according to their morphological characteristics: a, b, c, and d. However, the distinction of the types according to their morphometrics was not quite adequate. Finally, the bacteria observed in the cysts were circular or ellipsoid with double membrane, presenting a compact and dense distribution.
The present thesis is an extensive study of epitheliocystis in Greece and could be the base for further research on the disease and its causative agents but also on the prevention and treatment in order to eliminate its impact on fish-farming
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Μελέτη της επιθηλιοκύστης στην Ελλάδα
