Methylene Blue is effective against superficial fungal infections of fishes. The drug may be used as an alternative to Malachite Green for the control of fungus when it is known that the fish to be treated are sensitive. Methylene Blue is safe for use with fish eggs and fry for the prevention of fungal infections. As a secondary use, it is effective against some external protozoans, such as Ich, Chilodonella and Costia.
Clinical signs of disease: increased respiration; loss of normal body color; presence of discrete white spots; scratching on tank bottom or on objects; lethargic behavior; white tufts or strands on body; dust like peppered spots on body surface, having a yellowish cast.