Responses of mucus-producing cells in gill disease of rainbow trout (Oncorhynchus mykiss)

This paper documents the responses of mucus-producing cells in the gills of rainbow trout (Oncorhynchus mykiss) throughout a naturally occurring outbreak of bacterial gill disease (BGD) and following exposure to experimentally induced high concentrations of ammonia and suspended solids. The responses were examined at three sites on the gill filament with three histochemical stains selected to identify the main types of mucous glycoproteins; these were periodic acid-Schiff (PAS), alcian blue pH 2·5 (AB2) and alcian blue pH 1·0 (AB1). In the BGD-infected fish, there was an increase in the numbers of PAS-positive and AB2-positive mucous cells and a corresponding decrease in AB1-positive cells. The greatest increase in mucus-producing cells occurred at the tips of the filaments, but the greatest relative change occurred at the midfilamental (inter-lamellar) position. Fish exposed to high ammonia concentrations also had elevated numbers of mucus-producing cells, but there was no statistically significant change in fish exposed to high amounts of kaolin. The possible implications of these findings are discussed.