.a Sudden Mortality of Fishes Accompanying Supersaturation of Oxygen in Lake Waubesa, Wisconsin

A heavy loss of fish occurred during April 1940, in the south end of Lake Waubesa, Wisconsin, a•d i• the Yahara River below the lake. The fish affected were mainly black crappies, altllough bluegills, northern pike, yellow pikeperch, commm• suckers, and carp, were killed to a lesser extent. A heavy algal bloom composed principally of Chlamydomonas was concentrated in the area of fish loss and was accompanied by an extremely high (30-3'2 p.p.m.) oxygen content in the surface water. Characteristic lesions were present in the •qsh and consisted primarily of gas emboli in the gill capillaries a•d gas bubbles in the subcuta•eous tissues. Death of the •qsb was attributed to the blocking of the circulation through the gills by the gas bubbles with cm•sequent respiratory failure. A suggestion is made that oxygen was the gas forming the bubbles.