Will this work to Kill a Catfish?

Yeah, putting the catfish in saltwater for an hour will likely kill it. However, this seems needlessly cruel, even if you are planning to eat the fish. I'm not sure if the fish would suffocate or be poisoned, but either way it's not going to be quick. If you've decided to fish you should be responsible and not cause undue suffering to the fish you catch. This goes to angler ethics -- fish are a resource for us to harvest and utilize, but that doesn't mean we can treat your catch any way we want to.

I would tell you to use a fillet knife (or some other sharp knife) to quickly decapitate the fish (sever the spine), but you sort of need the head to skin a catfish. This doesn't have to be gruesome -- one hard, well-placed strike to the head with a club, hammer, or large rock will kill this fish quickly and humanely, even if the fish keeps moving. To me it would be much more disturbing to think of the fish slowly dying in a bucket as I drove home. And what if it doesn't die? What then? Put it in the microwave? You've made the choice to fish -- you at least owe the fish a humane end. Karma!

Your friends are sadistic or at least idiots. That they thought it was funny to pour salt water into a fresh water tank just to see what might happen is unbelievable.

Whenever you catch a nice sized catfish and want to bring it home for food, you obviously need to kill it but want to do it as humanely as possible. I admire you for looking around for a swift way. A hammer does work but it is hard to do, even for me. Putting the catfish in salt water would not work because most of the catfish I catch come from already brackish somewhat salty water and would survive. I have found that if I put the catfish in ice, their bodies cool down so they are less active. When that period is reached, you can dispatch them with a swift knife. Be careful for the sharp barbs on their fins. Also whacking them very hard with a heavy hammer will also work. Whatever you do, make it fast and sure. Cannot bring myself around to hammering them to a board and skinning them alive. That is unbelievably cruel.

If you want to be as in-humane as possible then yes that's one way of killing a catfish.

I really would recommend you DON'T do it however, hit it on the head with a heavy blunt object-you can buy an item called a "priest" from most fly shops which will dispatch most freshwater fish quickly and humanely.

Id say yes, try it.