Since the histopathological studies are recognized as biomarkers in the evaluation of the health of fish exposed to contaminants/ pathogenic microbes, metazoan parasites either in the laboratory or in the field studies, thereby the current work was undertaken to elucidate in more details the incidence of the different gill bacterial infections associated with contaminated water of Manzala Lake. The results of the present study revealed that the gills of bacterial infected fishes showed obvious distortion and erosion of the gill filament with internal haemorrhaged. Also, necrotic patches were detected on the surface of lamellae. From the histological point of view, the infected fishes exhibit many histopathological lesions including epithelial lifting at secondary lamellae, hyperplasia, fusion, and infiltration with necrotic patches of secondary lamellae. The gill epithelium was thin with extensive dilation of blood capillaries and swollen lamellae. Necrotic changes in gill lamellae were commonly noted. All the examined fish species collected from River Nile showed almost the normal pattern structure of gills at transmission electron microscopy observations. While the infected fishes displayed abundant distribution of mucous and goblet cells which characterized by dense cytoplasmic granules within their cytoplasm. Chloride cells appeared intact with cytoplasmic organelles and dense distribution of mitochondria. The apparent of chloride and mucous cell damage were markedly increased in Oreochromis niloticus comparing with Clarias gariepinus during both summer and winter seasons.
Key words: Fish, Bacteria, infections, Gill, TEM, Oreochromis, Clarias.
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