The prevalence of asymptomatic columnaris infection in black bullheads (Ictalurus melas) from Clear Lake, Iowa, during 1971 was the highest during the spring when the lake was warming, very low as summer approached and nil from July 28 through the autumn.

The mean condition factor of adult black bullheads decreased through the month of June and fluctuated at a lower level through the remainder of the summer and autumn. Mean hematocrit of adult black bullheads followed the same trend as that of condition factor. A positive correlation was evident between weekly mean condition factor and hematocrit (r = 0.90; P = 0.01).