Axolotl fat/bloated and barely eating

I have a 5 year old male axolotl who has always been a good eater. Once he reached adulthood he was eating 2-3 earthworms a week. Over the past six months, he has gone down to eating about half of a worm once a month. He will take a worm more often than that, but then he just spits it out. He is still a healthy-looking size though, which makes me think he must just be bloated. He is not floating and otherwise seems normal (not lethargic, no other lesions that I can tell).

His tank has sand substrate. In Oct I was concerned that impaction could be the issue so I fridged him for 3-4 weeks. He had 2 small poops, one with only a small number of sand flecks. I put him back in his tank hoping he would improve but he's pretty much stayed the same. A few days ago I removed all the sank from his tank just to be sure he couldn't eat any.

I included a picture of my set up. The most recent water parameters were (according to a fairly new API kit):
pH 7.4-7.6 (I have some crushed coral in his HOB filter to keep the pH up)
ammonia 0.25 ppm (this is also the value I get by testing tap water)
nitrite 0 ppm
nitrate 0 ppm
temp 15C

I have read that sometimes axolotls will go off their food for a bit, but this seems excessive. I'm worried about how healthy he can be if he is eating so little. Has anyone come across this before? Does he look bloated or am I overreacting?

Thanks for any help!

He definitely looks bloated imo.
One of my boys looked almost exactly like that after he ate WAY too much. I thought he was dying from bloat but I picked him up to move him into another tank and he puked up a bunch of his worms and old food.. and now he is good.

How long has he been boated like that?

He's been like this for about six months despite eating only a little bit of food infrequently.

Seems similar to this thread, give it a read and see if it sounds familiar to your situation

https://www.caudata.org/forum/showthread.php?t=79986

Yeah half a worm monthly is drastically insufficient.

Are you 100% sure he's male? I would assume by 5 you would know, but figured I would double check juuust in case. If he was female, the round-ness would be expected.

So, your parameters are perfect and fridging has not worked. This actually leaves you with very little recourse, unfortunately, aside from going to a vet. If it is impaction (which isnt likely based on what you have told us), fridging should cause it to pass IF it is able to. Other than that, it could be bacterial, renal failure, heart failure, or scepticaemia.The gills look heavily curled, and that might be a heavy tail curl too, so something is likely stressing him out. You COULD try salt baths in tandum with fridging?

Here is a resource:
http://www.axolotl.org/health.htm

I had seen the bloat post from jenniepeg but hers was so drastically bloated. Since I see mine everyday and since his belly is still technically as wide as his head, I wasn't sure if it was actually bloat or paranoia on my part.

I am pretty sure he's a male. At around 6 months old he was in a tank with one other axolotl (from the same clutch) and there were eggs three months straight. He had the larger cloaca at that time, although now that you mention it, his cloaca seems less pronounced than I remember.

Also, I realize those two earlier pictures made it look like his tail is always curved but that's not the case.

The only thing different this year is that I was able to keep him several degrees cooler this summer than usual. The past few summers his water was ~20-23C with fans blowing on the surface and this summer I was able to use air con to keep him below 20C. I think that's why it took me so long to finally realize there was a problem because I expected him to eat a little less at lower temps.

I too noticed his gills so I turned down the flow rate on his HOB filter, and I use a sponge to try to dissipate the waterfall. I also have a sponge filter because I travel fairly often and I'm afraid of the HOB not kicking back on if the power ever goes out while I'm out of town (this has happened a few times). I use another sponge to dissipate the air bubbles from the sponge filter. I am thinking I might just get rid of the HOB filter.

Thanks for the resources. I am getting ready to travel for the holidays but I will consider a salt bath/fridging when I return in Jan, and if that doesn't help I'll seek out a vet.

Just wanted to provide an update in case someone encounters the same issue. I made several changes to the tank: removed sand and HOB filter (kept sponge filter). I started feeding half a cube of frozen bloodworms at a time. He ate maybe one half a cube per week at first and then gradually started eating more, but still way less than I would have expected an axolotl to eat and still survive. After about 3 months on the bloodworms, he started showing more interest in food, like looking for food when I came in the room. I started feeding him small pieces of earth worms and he would eat about a quarter of a worm per week for a while. In the last few weeks his interest in food has increased tremendously and he has been eating 1-2 whole worms per week, and seems to be getting back to himself. He has not changed in size (no more or less bloated than my original post), and never got skinny from not eating.

I don't think I'll ever know exactly what the issue(s) were, but he came out fine after essentially going off his food for months and months.