Hope someone can help to solve this mystery! I have an 8 year old Black Moor, and on his tail fins he has a number of raised whitish spots. These spots have been there for some time (months rather than weeks), and they don't appear to be getting worse and the fish is otherwise healthy and feeding well. The spots don't look like either breeding tubercles (which would also be in the wrong place) and if it's a disease it doesn't seem to be spreading or getting worse. I looked at some on-line articles about lymphocystitis but again it doesn't look like the problem.
Any ideas on what's causing this or similar experiences would be most welcome!
I've attached a photo (for scale, the whole fish is about 7-8 inches long, from tip of nose to furthest point of tail.

Lovely fish. Given the duration of the spots and the fish otherwise seeming well, I think it's likely just part of how the fish is developing over time - my goldfish (when I kept them) and tropical fish (kept in more recent years) have each changed slightly in appearance over the course of their lives including specks on the caudal/tail fin and other characteristics. Unless the fish's behaviour changes or additional problems arise, then I wouldn't be concerned.

It is always important to ensure that water quality is 0 ammonia, 0 nitrite and <20 nitrates (or no more than 20 above tap water nitrate levels). If any of these are out of kilter, then the fish could display signs of the onset of an illness, so, and especially as the fish ages and is at risk of succumbing more quickly than when younger, it's definitely worth monitoring these regularly and it may be that larger and more frequent water changes have to be done.

Hope that helps.

Thanks for getting back to me - it's much appreciated

It doesn't look like anything serious, from what you said. The fish is already undergoing a transformation from matt black to lighter black with gold patches, so hopefully the lumps are just benign consequences of getting older...!

I keep the nitrates below 40 (tap water is 20 round here), and the water has no trace of ammonia or nitrates.

Thanks again,

Steve

Hello Stevet- Did you ever find out what the spots were? Did your black moor survive? My ranchu has developed the exact same thing and no one seems to know what it is. I am not sure how to treat / medicate my ranchu or if it is even needed. Thanks!!