Columnaris, caused by the bacterium Flexibacter columnaris, is a fish disease and it is not contagious to humans. The bacteria that causes columnaris is specific to fish and cannot infect humans. However, it is important to practice good hygiene when handling fish or water from an infected aquarium, as the bacteria can be spread through contaminated equipment or hands. It's also important to not consume infected fish, as the bacteria can cause food poisoning if the fish is not properly cleaned and cooked.