Fish - Swollen Abdomen but acting normal

Hi all! Apologies for the essay below - I am at loss what to do!

I am looking for some advice, I have exhausted my local fish specialists at our local aquarium shops and there seems to be no fish vets near me.
I have a 148-ish gallon tank with 6 goldfish in it (and a couple of mystery snails). We run a sump system, no fish have been added for at least a year and the fish in question has been in the tank for almost two years.

I have recently reset out sump system as I wasn't happy with the filtration set up, ammonia was slightly high (not at 0 but less than 0.25) but I have done significant water changes since then and we are almost back on track to optimal conditions.

The fish in question is my largest fish in the tank. No other fish is exhibiting any changes so I am thinking this isn't an issue with the tank/something contagious.

I went away for a fortnight in April. During this fortnight the person looking after my fish was called away for a few days so I asked them to put in a holiday feeder. When I returned from my trip I noticed this fish was slightly swollen. I asked when this had happened and the person looking after my fish said they believed they saw the fish eat the rest of the holiday block once it was small enough to be swallowed whole. Since then, however, my fish only seems to be getting larger.

I gave the fish a few weeks incase it was just some plump-ness from being overfed while I was away. The fish however has not had any change, so in the past month I have done the following

- Whole tank parasite treatment
- Reduced food to the whole tank and introduced more fibre rich foods
- Approximately 10x salt baths for the affected fish with nothing passing
- Added a heater. I am in Australia and we have come into a fairly cold winter, I have added the heater to try and simulate going into warmer weather incase the fish is eggbound
- Did a 2.5 day fast for this fish, with it then being only fed blanched peas for a day after the fast.
- I have very gently tried to express any eggs, following a few guides from vet videos I have found online. Nothing has been expressed however I haven't attempted this before so I may be being too gentle/not doing it properly.

In the past week I have noticed a red lesion on the anal fin however it is the only fish to have this, so I am unsure if it is related. Fishes scales are still flush to the body, and the fish specialists near me agree it is most likely not dropsy. Fish still have an appetite, still swims around with the other fish however in the past few weeks it has seemed that the fish will go rest in a corner of the tank more between feeds and after swimming with the other fish for a bit.



Any advice would be greatly appreciated. I'm not sure if I just need to wait to go further for the fish to develop/reabsorb the eggs if it is eggbound, or if it is just a fat fish now or if there is possibly internal tumors or something else going on. Thank you to anyone who has read this far.


I have attached some photos of the fish, please ignore if the glass/water is appearing dirty - in the middle of a water change and am moving all their decorations around!

My suspicion would be an intestinal blockage, but a partial one. If it were kidney failure the scales would be pineconing. Since it swallowed a feeder block, a perforation might also be possible, and there could be an infection. The block may have dissolved and passed, but it may have done internal damage.

If the caudal fin gets streaky, then the possible infection is in the blood.

First, I would stop feeding the fish for a week or two. I am in a no antibiotics over the counter zone, so no suggestions there. I'd watch and wait and see, and not be optimistic.