What happens next?

How to humanely kill a fish
Ask a veterinarian if possible.
There are many species of aquarium fish, and for most of them the ideal drug dosages and other conditions are unknown. A veterinarian is trained to notice signs of suffering and adjust the process if necessary, giving your fish a less painful death.

Pick your answer from:
(1). If you live in an area where fish is attacking other fish, you may want to fish instead of fish. Ask your veterinarian if you can cut open a fish as long as you don't see a vein running through it..
(2). Only methods reasonable to perform at home are included in this article. Other methods, such as electrocution and lethal injection, are difficult to perform humanely without training, and/or can harm the person performing them..
(3). It's also a good idea to ask any questions that might arise regarding your own aquarium animal population. Many aquarium dwellers act as babysitters, contributing to the conflicts among the fish's relatives..
(4). Tap the fish in your hand using an ice cube tray, or get a special glass container and place it in the fridge. Set the temperature to the lowest temperature possible..
(2).