Axolotl losing gill filaments

Hi

I have three axolotl in a 120L tank. They are about 9 months old, I have had them for 3 months. I have one wild and two leucistic.

One of the leucistic ones had a legion on it's arm about two weeks ago, it looked like he had scraped it on a stone that he hides in and it seemed to clear up fine.

Today however I have noticed that on one side he has lost most of his gill filaments I can't see any other physical symptoms and he's pretty lethargic most of the time so it's hard to judge his behaviour. He is eating fine. I did notice this morning that he pooped out a mucusy see-through poo which I have never seen before, pretty sure it's not a sperm packet.

The other two axolotl are fine and showing no signs of gill degeneration. I'm pretty sure the gill filaments loss is not due to one of the others biting him as the bits that the filament stem from (the spike bits) are all perfectly formed still. If the damage were due to a bite I don't think it would look like it does. It literally looks as though the filament has dissolved on one side.

I have tested the water today and got the following -

ph 7.2
Carbonate hardness 10
General hardness 14
nitrate 250
nitrite 0

I also bought a kit to test the ammonia today as I was worried it might be that. That was between 0.5-1.0 ppm which was in the 'stressed' section.

What are peoples thoughts on what could be causing this?

Many thanks

My guess is that it's due to the ammonia. Is it possible theres food or poo in the tank that might be causing the spike? I don't know if your tank was cycled to begin with but it sounds like you'll need to cycle it again. In the mean time try to keep ammonia low with frequent small water changes. You can add bottled beneficial bacteria to try to speed things up, and Prime's water conditioner binds ammonia which could be helpful.

It could also be due to bacteria and/or single celled parasites. This recently happened to my axolotl and the parasites were eating away at my poor axies gills. I went to the vet and was prescribed medicine and now my axie is back to normal. I would recommend a vet visit if possible. Did you notice any white growth on the gills or white patches on the body?