Fish death caused by gas bubble disease: a case report

This work summarises the findings of an investigation on a local trout farm (Czech Republic), which was carried out in connection with the repeated deaths of salmonids (brook trout, Salvelinus fontinalis and rainbow trout, Oncorhynchus mykiss). These fishes were reared in newly installed tanks that were supplied with water from the same source as the original outdoor nature pond where the fishes had been reared without problems. The skin of dead fish was pale and covered with a thin layer of mucus. The gills had lighter colour, and microscopically, gas bubbles were visible both on the surface of gills and inside the gill filaments. No changes were found in the body cavity and parasitological examination was negative. The water in the tank was of very good quality but its oxygen saturation reached 136%. Based on the results of fish examinations and water analysis, gas bubble disease was identified as the ultimate cause of fish deaths. After making technical adjustments (technical changes to the pumping of water from the spring and ventilation of the storage tank in the building) oxygen saturation in water remained below 100% and no further cases of gas bubble disease (or fish deaths) were recorded.