Malachite Green is used to treat fungal infections. Malachite Green is directly applied to the fish body as a 1% solution (1g in 100ml of water). For smaller fish, a 0.5% solution can be used.
Malachite Green also protects eggs of fish from fungal infections. However, there are controversies surrounding this drug. Some research suggests a link between malachite green and cancer symptoms in rats.
This has led to this drug being banned in the aquaculture industry.