According to the Fish Channel, fish can regrow lost scales. Scales grow back quickly on the majority of fish without the need for treatment or medications.
The Fish Channel suggests that preventative treatments and medications, such as antifungus and anti-finrot drugs, need to be given if blood is present or if the muscle tissue is visible from the scale loss. This helps fight against fungal infections and bacterial infections.
Wild-caught fish may sustain scale injuries during the capture process, while fish in an aquarium may injure their scales while attempting to avoid handling, such as for cleaning the tank. Fighting with other fish or unsuccessful predation cause injury to scales as can collisions and abrasions.