The way we commercial guys do it is by making a slice by the tail and snapping the bone, all the blood will run out.Make sure the fish is in water when you do this.Use a cooler and fill it with water cut your fish by the tail snap the bone and let him swim in the cooler and it will bleed out.Works every time. We do it with fluke it works great.
I've heard of that with catfish, seems like a good idea, the spine must have a lot of blood running through it and the fish attempting to swim must help the matter. I'll have to try that some time.
I usually stick two fingers into the gills and rip them out, then wave the gills in the air and yell like an Indian. It's probably no more effective then using a knife or scissor but it's definitely more fun
.........oh yeah, beer helps with the fun factor.