Preservation of mucous biofilms of fish gills and skin: potential diagnostic and research applications

Healthy gills from fingerling rainbow trout were dissected and fixed using either a conventional 0.1M cacodylate buffered 2.5% glutaraldehyde or the same fixative with 2% (w/v) Alcian blue added. The tissues were processed for light and electron microscopy. Skin tissue samples from cases of necrotic dermatitis were prepared in the same way. The conventional fixative provided excellent fixation of cellular architecture but poor preservation of a mucous coat in both cases. The addition of Alcian blue provided excellent preservation of both cellular architecture and mucous coat. There was little evidence of bacteria in the mucous coat of the healthy gills although some zoospore-like structures were seen attached to the gill epithelia. Skin samples from the dermatitis sample demonstrated a profuse biofilm associated with the necrotic lesion which had not been visible with conventional preservation. The technique offers a cheap rapid method for biofilm preservation which will aid in diagnosis and study of surface disease pathogens..