What physical ailment are you seeing? If you're talking about the black patch on the front of him, to me that looks like coloration. Like hes supposed to look like that. However, if you purchased him as a red fish and now he's got that black patch on him - that is unusual.
Though, that's usually not a disease. Have you testing your tank water recently? sometimes when the ammonia gets too high in the aquarium, it can cause ammonia burns on your fish and those look like black or grey....patches along the fish's scales.
Another thing I notice is that it looks like his stomach is a slightly lighter color than the rest of him. Is he just full and that's light reflecting off his scales, OR he could be coming down with an external bacterial infection. I really think its just the light/ color there though.
Another thing too, did you purchase him as an adult? or a juvenile? Sometimes it takes awhile with livebearers for their colors to come all the way in. Goldfish do the same thing too, I used to have a black, orange, and white goldfish, now he's all orange.
It's more of a dark red patch. It almost looks like blood. I tested my water yesterday with ammonia, nitrite, and nitrate all at 0. About the stomach, he has always looked like that. It's just the coloring on his batch. He was born in the tank he's in now and is about two years old. Thank you for your help
Ahhh, I see that now. Wow. Is it almost rising off of the black? like small blisters? Ooooo, I've never seen anything like that before either but.....
There is a type of bacteria that causes...basically capillary rupture. Most times it occurs in the fin rays (where the rays in the fin turn red bec. a blood vessel has burst in the fin) It can also occur on the body. Generally the name it goes by is hemorrhagic septicemia and is described as 'red streaks along the body'.
I can't diagnose it, I'm not sure what it is...but from my experience, I would guess its being caused by some type of gram negative bacteria. I mean, if it just looks like a scratched spot than...it's possible he literally got stuck somewhere and scraped himself. But if the patches look like they've got a structure to em...if they're not just random that I would guess its a bacteria. I don't know of any parasites that would cause that. and its DEF. not a fungus.