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A few weeks ago I noticed that the orange spots on my white/orange koi seemed to be fading. Other than that he was acting completely normal. I had to go out of town for a month and told my roomate to keep an eye on him. When I came back he was still acting normal, but all of his orange spots were completely gone and now he is a silvery white color with a very light orange tint. I was just wondering what may have caused this. I have a 10 gallon tank that has been established for several years and I only have three fish total (my koi, and two goldfish)and while I have been having a small brown algae problem lately nothing seems to be awry with the tank.

On another note, one of my goldfish has had a white growth on his head for several months now. His behavior is not erratic at all and none of the other fish seem to be affected by it. I have searched several disease sites and found nothing similar to it. Any thoughts?

A koi in a 10 gallon? We are talking koi as in 'pond fish'? When did you perform the last water change?

i guess fish just change color. my male guppy's (who is on the brink of DEATH) tail went from blue to yellow with a blue center, over and over.....

What came first? the chicken or the egg? No really.....

Koi do change colour, although I'm unsure of how quickly that normally happens.

Can you describe the white growth a bit more? Any chance of a photo?

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

Looking into it more I actually found that it isn't unusual for koi and goldfish to change color as they mature (who knew!). For more info on that here's a site to check out (one of several like it that I found).

http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=2735&cid=3783&search=

As for my goldfish with the growth, I will try to get a picture, but honestly, it kind of looks like a mini lionhead growth on his head. It is about 4-5 mm in diameter and like I said doesn't seem to bother him at all.

In that article they actually neglected to mention the most common causes of koi and goldfish (and the various captive bred derivatives) colour changes. Most fish colour is predetermined by genes, and both koi and goldfish colour genes are not 100% stable, being that the fish are the colour we admire them for today as a result of selective breeding, which compared to natural evolution is notoriously fragile method of instilling a permanent characteristic on a fish.

Recessive genes will become dominant in some fish, resulting in the colours we admire, but the natural colour genes are far more dominant and likely to re-emerge over successive generations not so carefully monitored for selective traits. Occassionally some goldfish for example , give birth to natural bronze-brown coloured young, and there is also the issue of hormonal changes being written into the code having an effect on pigmentation.

With the first flush of mature hormones its not unusual for a fish in any of these groups to change pattern, become more melanistic, or indeed fade. Some goldies change from silver or white to gold, black moors often go gold when they mature. It has been theorised that if you took a batch of goldfish, threw them in a lake for 300 years and came back to see what colour they were, nature would have reasserted itself, predation and partner selection would have taken place and more than 80% of the remaining fish would have completely reverted back to normal brown colour for the species.

In short ,these forces are always at work multigenerationally in almost any population of goldies or koi, and its the less rigorous exponents of captive breeding that have failed to completely extinguish any chance of natural reversion. Goldies and koi are bred on the principles of mendelian genetics (basically guessing the morphological potential of parentage) rather than genetics proper , and as such , a touch of the wild remains in goldies and koi, and they are still able to change, vary, and evolve, even revert to originator morphology. The changes can even happen in a single fish as it ages. Actually its a good thing for fish health, but no doubt some owners do get stung, just having paid out several hundred or thousand bucks for a koi with specific traits.

Serves em right for being so bloody dippy over a fish

I rather like the irreverence of nature

I'm not that up to date with goldies, but I believe that the lionhead growth is a type of tumour. If it is that, I guess it depends on where it is situated as to how much of a problem it is. Looking forward to the photo

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett