Gross pathology photograph of the gills of a goldfish (Carassius auratus) showing a creamy material. A gill biopsy of this material should be examined via a wet mount. Columnaris can be diagnosed or ruled out if other bacteria are involved. The fish in this image was euthanized due to other health concerns, but gill biopsies can be performed using a non-lethal technique.
Courtesy of Dr. Denise Petty.