The Goldfish Sanctuary
Ich (aka Ick, Ichtyopthirius, Freshwater White Spot Disease)
Symptoms: body and/or fins are covered with tiny white dots, rapid gill movements possible in late stages
Ich is one of the more common afflictions of goldfish. Left untreated, it can be fatal to your fish, and because treatment takes many days to work, every moment counts. Ich is highly contageous.
The disease is easy to spot. The white dots are small and sometimes numerous, about a millimeter each. They are easiest to see on the fish's transparent fins. When on the fish, medications have no affect on Ich. As the parasite grows, however, it will eventually drop off the fish to reproduce. At the bottom of the tank, it will form a cyst (also resistant to medications) and soon hatch into hundreds of baby parasites which will seek a new host animal. This process weakens the fish and leaves holes in the fish's body. A badly afflicted fish will likely display rapid gill movements.
Another note: although many may suggest raising the water temperature to speed treatment, this may not be necessary if you are able to catch the disease early. It is better not to raise the temperature to a high level in a goldfish tank unless their lives depend on it. If in doubt, consult your local petstore or vet.