What does it mean when a goldfish has white on its head?

Ich is a common disease in goldfish which causes them to develop small, white spots on their heads and fins. It can also be found on the body and tail. The spots are caused by a parasite called Ichthyophthirius multifiliis. The parasite lives on the fish's skin and gills, causing irritation and damage. Ich can be treated with medication and salt baths.