One of the most likely causes of your Common Goldfish contracting a disease is from the water where your goldfish is housed. Either due to the poor quality of the water due to the waste your goldfish has produced. An overcrowded bowl or tank can also contribute ill health to your goldfish.
Another very common cause for your Goldfish to become ill is if you or someone else overfeeds your goldfish.
For symptoms of disease you should look for cuts on your goldfish's fins, changes in the color of the eyes and scales, scales dropping off, and also look at the nostrils for excretions.
A common indicator of whether your goldfish is unwell is if it often journeys to the top of the bowl or tank.
