PlanetCatfish.com

http://i.imgur.com/ONTXNZ7.jpg
About halfway down, next to the dorsal fin. The owner says it comes and goes in different spots but the pleco seems healthy.

Can you get a closer photo? Could it be something like fish mites? (I don't know, I'm just guessing) I might guess a fluke, but most of the flukes I am familiar with are subcutaneous, and they wouldn't disappear and reappear as you describe.

Hi,

Could you post the temp of your tank please.

"To answer their questions: it's not fish mites or flukes, because it's level with the skin. It's just a discolouration of the skin that disappears and appears at random. The tank temp is about 25C/77F. I tried getting better pics, but he's mostly hanging out in the back."

mellor21 wrote:"... it's level with the skin. It's just a discolouration of the skin that disappears and appears at random."

Since of course we can't see the actual fish in life, I'll take your word for this. In the photo you provided, the white spot appeared to me to be 3-dimensional, with a slight arch to it. That's why I suggested mites or (less likely) flukes.

bekateen wrote:

mellor21 wrote:"... it's level with the skin. It's just a discolouration of the skin that disappears and appears at random."

Since of course we can't see the actual fish in life, I'll take your word for this. In the photo you provided, the white spot appeared to me to be 3-dimensional, with a slight arch to it. That's why I suggested mites or (less likely) flukes.

She got some more pictures for you guys if that will help
http://imgur.com/a/CXw6e
http://i.imgur.com/bxkQYBs.jpg

mellor21 wrote:The owner says it comes and goes in different spots.

Does it always appear in the same locations? In other words, are there a specific number of spots, and they simply fade and then come back? Or do the spots seem to move around the body, in different locations? Is it just one spot, or are there several at once? (in your photos, there appears to be a second spot dorsal to the pectoral fin)

bekateen wrote:Does it always appear in the same locations? In other words, are there a specific number of spots, and they simply fade and then come back? Or do the spots seem to move around the body, in different locations? Is it just one spot, or are there several at once? (in your photos, there appears to be a second spot dorsal to the pectoral fin)

"For the past year, I thought the spots would appear at random. But it looks like they mostly appear next to the dorsal and pectoral fin. Currently, there's also a small spot on its snout, but it wasn't there a few weeks ago."

Edit, also this
"The spots don't fade and reappear over the course of a few hours, I think that they take 3-4 days to change"

If they don't move, but simply fade and return, and if they aren't 3-dimensional (bumps), I'd guess they are simply spots - maybe slight aberrations of natural color (just like people can have areas of skin with more or less pigmentation) or perhaps scars from old wounds, which didn't heal with normal coloration. That's just my guess.