Meekaboo said:
Ok, so it's 'normal'. But why does it happen? Can anything be done to prevent it or to make it happen? Does it affect the fishes health? My rather plain orange goldfish with a slight white belly took about two weeks to turn totally white recently.
Sorry about all the questions but I've asked at various pet stores over the years and nobody ever knew any of the answers. I even asked at a large local store that specializes in fish and they either didn't have a clue of couldn't be bothered to explain it to me.
Goldfish MAY change color throughout their lives. A few years after birth or when the goldfish (single finned varieties) reach 4 to 6 inches in length (3 to 5 inches for fancy goldfish), they should have obtained their best colors. What ever color your goldfish is, or will become, it is at its brightest and best in an outdoor pond.
Goldfish and many other animals change color in response to light levels. Pigment production in response to light is something we are all familiar with, since this is the basis for a suntan. Fish have cells called chromatophores that produce the pigments that give coloration or reflect light. The color of a fish is determined in part by which pigments are in the cells (there are several colors), how many pigment molecules there are, and whether the pigment is clustered inside the cell or is distributed throughout the cytoplasm.
Goldfish tend to change color. Most change during the first year of life, but others change throughout their lifetimes (which should be at least 10 years). Inexpensive goldfish change in unpredictable ways because their parentage is uncertain and their color genes represent a random mix. Expensive "purebred" goldfish SHOULD exhibit significantly more predictable changes, achieving similar coloration of their parents as they mature. But be warned: If you purchase young (under a year or so), high-quality goldfish you cannot be certain that the colors you see are the colors you will end up with a year later.
Most importantly, color change in goldfish is not harmful to a fish; it is not an indication that something is wrong, and it is not a disease. Treating healthy goldfish with antibiotics is a sure-fire way to kill the animals (and guarantee one final color change).
