EVALUATION OF BIS(TRI-N-BUTYLTIN)OXIDE (TBTO) NEUROTOXICITY IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) .2. ULTRASTRUCTURAL DIAGNOSIS AND TIN LOCALIZATION BY ENERGY-FILTERING TRANSMISSION ELECTRON-MICROSCOPY (EFTEM)

Three week-old rainbow trout hatchlings (Oncorhynchus mykiss) were exp osed to 0.5 mug/l or 2.0 mug/l bis(tri-n-butyltin)oxide (TBTO) for 21 days in a flowthrough system. After 7 and 21 days, tissue samples of t he brain (tectum opticum and optic nerve) were taken and processed for electron microscopical investigations. Ultrastructural lesions in the tectum opticum and the optic nerve included: intramyelin vacuolizatio n in the stratum opticum and the stratum album centrale of the tectum opticum and also in the optic nerve; darkening of fibres in the stratu m opticum of the tectum opticum; necrosis in regions of myelinated and non-myelinated fibres in the stratum opticum and stratum album centra le; and an increase in the number of dark cells in the stratum periven triculare of the tectum opticum. In animals treated for 21 days with 2 mug/l TBTO, tin could be identified in endothelial cells and myelin s heaths by means of electron spectroscopic imaging (ESI) and electron e nergy loss spectroscopy (EELS).