I've probably mis-judged the tone of this thread, but...
If you're serious about euthanising the CAE, make sure you do it ethically...
Clove oil or temperature shock (not the same as freezing the fish) are probably the most easily accesable... Flushing it down the pan, or tossing it in a SW tank are deffinitaly not acceptable solutions to the problem....
I'd reccomend temperature shock.. Take a container large enough for the fish, fill it with water and place it in the freezer. When it's right at the point of freezing (maybe a little slushy) take it out and drop the fish directly into it... Fish won't feel a thing... Make sure by puting the container + fish back into the freezer overnight...
Then you could defrost the fish and feed to your other stock assuming it was healthy, will be completely fresh still... I wouldn't risk feeding the dead CAE to your stock if you used clove oil however....
Like I said I may have completely mis-judged the tone of the thread... Just offering cautios advice!