Mystery illness...

[Megalodon]

First off: This disease... It's very strange but not contagious, the symptoms occasionally look nasty but don't seem to affect the fish. Only occurs in female Danios that are related so I'm not 100% sure if it's a genetic illness (potentially sex-linked) in some way rather than pathogenic and I've tracked the first symptom of the disease back to over 4 years ago in the eldest Danio. This Danio is still alive, it's been through treatments for pretty much everything... The only things I haven't tried are salt and antibiotics. I have just kinda accepted its there. I can't take photos but I'd be really grateful if someone could ID this disease, I have looked in every book I can get my hands on and looked all over the Internet but cannot find exact matches. These symptoms are across the 3 Danios, one Danio is still a Juvenile which showed them since early development, becoming more severe when maturing:

- Swollen stomach equally on both sides with no standing scales or trouble swimming
- Ruptures/"blood veins" on the under-belly of the fish that heal after a few days. They look like the fish has been slit with a knife repeatedly and is bleeding but no fluid is actually leaking out as far as I can tell...
- A large black "smudge" across the side of the Danio
- "Scar tissue" randomly appearing and very severly. No leeches in tank, 100% sure no rubbing/injuries caused these and it looks like you've ripped a chunk out of the fish... It's open and nasty, happens spontaneously but heals within a few days. Covers anything from a small patch on the side to almost the whole one side of the fish and entire underbelly... Can occur on both sides. The "smudge" occurs after healing and before it seemingly erupts from nowhere.
- Swollen anus; No internal or external parasites.
- Ulcerations
- Disfigurement (one has an 'S' shaped stomach with no spinal deformities)

Purely out of curiosity really, I don't have any intentions to euthanise them because despite everything they're healthy, happy fish. They've been through quite a few setups, I did a complete Fishless cycle for over a month to the first tank they were ever added to, they have never contracted fish TB (you could probably guess that) and I've never really had any water troubles or ever had a tank too small for them.

I don't remember if I got them like this to be honest, I must have really but I can't remember any distinct moment beyond first noticing the oldest fish "tearing apart" over 4 years ago. So yeah, I'll say first thing I noticed was the bleeding stomach which looks like the fish is going to split in half down the middle. There's a long line of "blood" running vertically down the entire underbelly with blood-filled "cracks". Can't really explain much better than that. No other Danio nor any other species has "caught" this disease and they seem to be able to breed.

Ideas on what the disease could be?

[escamosa]

That sounds absolutely horrible! Some of the things that you have described fit in with fish TB, some them fit in with dropsy. But really I haven't a clue on what else it could be. Poor little things.

[madagascariensis]

I thought of some twisted version of neon tetra disease(yes it affects danios too)
that would explain why no other tankmates are affected. It however would not explain
why only female danios get it. I would say that it is some kind of genetic weakness since it appears extremely specific about its victims.