Not all goldfish are gold! Even a goldfish that starts life a bright shade of orange may change colors throughout his life. There are different reasons why a goldfish may change colors. Diet changes, poor quality food, and parasites can leave you with a fish of a different color.
Genetics play a big part in goldfish color. Moors (black goldfish) may be cross-bred with telescopes (goldfish of any other color) to improve body shape or vision. The baby goldfish from a moor/telescope breeding may or may not change colors. Some baby goldfish stay black all their lives. Some change colors only on their bellies; others turn gold. The color change may happen within the first six months of life. It may take years for a color change to happen.
Some goldfish change colors temporarily. Just like a human can get a bruise after an injury, a goldfish may show black patches on the body or fins as a sign of healing. The trip to or from a pet store can be strenuous for a goldfish! As your fish starts to settle in and heal, he may develop black patches. This is only a temporary color change; your goldfish should be back to normal within a few weeks.
One color change that is a serious health issue is dullness. If your goldfish’s color becomes very dull and he seems to be a lot less active, you could have a big health problem on your hands. Parasites, chemical imbalance in the tank, and digestive issues can all result in a color change. Watch your goldfish after an illness where you have administered antibiotics; a color change could signal that the antibiotics have harmed “good bacteria” in your goldfish’s system. Without good bacteria, your fish cannot digest his food. Ask your aquarium supplier about probiotics for your goldfish after an illness to promote the action of good bacteria.
Most of the time, a color change in your goldfish is perfectly natural and nothing to worry about. However, if the change is a dulling and not an actual color change, you may have an actual health issue on your hands.
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