As to whether or not it is suffering i wouldnt know..but i know 2 ways to humanely kill a fish, first option is to put the fish in a container with some water and put a bunch of alkaseltzer tablets in it...this will cause quick afixiation due to the carbon dioxide from the tablets, the second option is to freeze the fish.. put the fish in a container in some water and add a couple ice cubes, then put the container in the freezer. Good luck with whatever you choose to do