Figure 3
From: Columnaris disease in fish: a review with emphasis on bacterium-host interactions
F. columnare induced a saddleback lesion (arrow) in rainbow trout fry. The lesion is visible as a discoloration starting around its common location at the base of the dorsal fin and extending laterally to encircle the fish resembling a saddle. Hence, the descriptive term “saddle-back” is often used and the disease is denoted as “saddle-back disease” (bar = 1 cm).