Acriflavine is a preventative and treatment for the control of Oodinium (Velvet) in freshwater and marine fishes. It has a long history of usefulness for the control of fish diseases. Acriflavine is useful for fish egg disinfection, treatment of open wounds, and external protozoan infections. The drug is effective in the control of the bacterial infection "columnaris" (Flexibacter columnaris). Acriflavine may also be considered as an alternative to Malachite Green when it is known that a certain species of fish may be sensitive.