Should I just euthanise him?

Do another small water change in a day or so and fast him for a few days if he is still eating. Could you post a picture of him?
We have a tenant currently who's in my room with fish tanks, I should be able to post a photo or two.Though I have made couple days ago a photo of him; he's still bloated there and looks like he looks now, but only shaky moves and lays around:

IMG_20200829_140129.jpg
You can kinda see how he's bloated there ^
 
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