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Title: Ultrastructural and morphometric studies on the gills of the freshwater fish Gnathonemus Petersii (family : Mormyridae) exposed to selected pollutants
Author: Al-Azemi, B. M.
ISNI:       0000 0004 2692 501X
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1996
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The histopathological effects of three heavy metals, cyanide and atrazine on the gill tissues of the mormyrid fish, Gnathonemus petersii, were determined primarily by electron microscopy. Replicate samples of fish were exposed for 6 hours to acute and subacute concentrations of each toxicant in a continuous flow system comprising aerated, dechlorinated and heated water. Specific alterations to gill ultrastructure were found to be associated with each toxicant. Cadmium damage at 1.0 mg 1.1 was associated with the formation of large subepithelial spaces within the secondary lamellae and at 10.0 mg 1,1 with lamellar aneurism. Chromium caused epithelial hyperplasia at 1.0 mg 1'1 and extensive fusion of secondary lamellae at 10.0 mg 1'1. Copper exposure stimulated hyperactivity of mucous cells at 0.1 mg 1'1 which resulted in the accumulation of a thick layer of mucus on the gills at 0.5 mg 1,1. Cyanide caused desquamation of filamental epithelium at 0.05 mg 1'1 and stripping of the epithelium and underlying tissue down to the supporting cartilage at 0.1 mg 1'1. Atrazine damage was characterized by the presence of breaks in the gill epithelium at 0.5 mg 1,1 which developed into deep pits at 5.0 mg 1'1. Morphometric measurements of the structural components of secondary lamellae revealed quantitative differences in tissue alterations among fish exposed to different toxicants. A significant increase in the volume of secondary lamellae has been found in fish exposed to heavy metals. On the other hand, fish exposed to atrazine and 0.1 mg 1,1 cyanide showed a sharp decrease in lamellar volume. The increase in lamellar volume in fish exposed to heavy metals was also accompanied by a reduction in the interlamellar water spaces and a significant increase in the water-blood diffusion distance. In cadmium-exposed fish the increase in lamellar volume was mainly attributed to the increase in the subepithelial spaces at 1.0 mg 1'1 or in the volume of blood components due to aneurism at 10.0 mg 1'1. In'fish exposed to chromium it was attributed to the thickening of the epithelial layer as a result of epithelial hyperplasia; or epithelial hypertrophy in copper-exposed fish. On the other hand, the decrease in lamellar volume in fish exposed to 0.10 mg 1'1 cyanide was mainly attributed to the decrease in the volume of the tissue-occupied region outside the basement membrane due to the stripping of lamellar epithelium. In both concentrations ofatrazine (O.S and S.O mg 1'1) the different components of the secondary lamella contributed to the decrease in lamellar volume. These morphometric analyses confirm observations made by electron microscopy. The present study, therefore, demonstrates the potential of electron microscopy, in particular SEM, as a tool for detecting pollutant-induced damage to the surface of fish gills. Preliminary work with chromium has indicated that comparative ultrastructural studies are now needed to further our understanding of the chronic exposure of fish to these toxic chemicals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available