They obviously don't know how to kill a fish.
Two best options
1) club (fish bonker, billy bat, ASP, etc) one or two swift, strong strikes to the top of the skull, does the job instantly, works surprisingly well even on bigger fish up to and probably beyond the 50lb range.
2) cutting the gills. usually bleeding a fish is done to keep the meat in pristine condition when eating is a factor, but it also kills the fish in much more timely manner than stabbing a fish in the side.
Those asian carp are hardy, and one very well might survive a single stab wound to the side.