The use of Methylene Blue is primarily for the control of fungus on eggs, and to assist the transport of oxygen in fish poisoned by cyanide and nitrite ion. Secondary uses are for the control of some external protozoan parasites of fishes. Methylene Blue is an alternative for treatment with other medications when prevailing factors preclude the use of another medication.
It's a firemouth, don't know anything more specific than that. I just saw it on the net somewhere and stole it for myself. The bad thing is, on my home computer, the fish actually looks like he's making a mean face and you can't tell on the avatar.