Exactly the same thing happened to my Danio sadly he passed away wilst we were on holiday. I wish I had of just euthenised him before we left.
Gamwar
Please just humanly euthenise him/her.
Here is how to:
-Get a container of some sort mabye an empty margerine tub or somthing similer,
- Fill it with tap water,
- Put it into the freezer,
- When it has a thin layer of ice over it,
- dip him in. All of his organs will shut down almost emediatly.