Question: Axolotl Has A Lump

[veeveeiey]

Hello! This is my very first time posting on this website, and it's helped me out very much in acclimating me into getting my very first axolotl. I picked him up at a reptile expo from a reputable breeder, so I'm fairly certain he wasn't sick or anything when I first got him. He's been doing great: I have him in a 20L with a constant temp between 60-65, plenty of hiding spaces, very fine sand for substrate, he's been eating rather little but very eagerly (chopped up earth worm), tank parameters are good, and he has no gill or tail curling!
But for some reason, out of nowhere, he began to form a HUGE lump on his left side, and a significant dent on his right side. I have no idea why because he seems to be doing great, but it's developed very quickly over the course of a week and half. Despite his body looking horribly deformed since he's so little (8 1/2 cm), he seems to be doing just fine! But it just looks so bad, I don't know what I could attribute it to. My small theory is that maybe I'm inadvertently underfeeding him? He does this thing where he'll eat about three pieces of earthworm and done, and I think he's full and I read that babies eat once a day so I call it, but in fact maybe he's still hungry? I don't quite know what it is yet, I'm still so inexperienced but I'm deeply worried about him!! I hope I don't sound super silly and I'm just missing some common knowledge thing amongst experienced keepers! Please help!
The first picture with black circles was taken on September 24th, showing his smooth sides. The second picture with the red circles was taken just yesterday, and it looks horrible!!

[Hayley]

Have you noticed if he's been pooping okay? I'm not entirely sure what may be causing it, potentially digestion issue. The axie is pretty small so watch for him eating sand as it can cause impaction in little guys.

[veeveeiey]

Funny you should mention, I just cleaned his tank out and he’s pooped twice- and his body is back to normal!!!! I guess he was just a little backed up? Thank you so much for your reply!

[Hayley]

Great! Must have been digestion then. Watch out for it in future but if it's gone I wouldn't really worry :)