I feed live mice to snakes in the event they wont eat frozen, the death is not instant, but when compared to watching fish kill a mouse, it is much quicker.
If you have ever watched a video of a piranha killing a mouse, you'll understand its a terrible death for the mouse. Im not an activist or anything, I hunt, I feed live when nessesary, but in a case like this, IMO the death of the mouse is too cruel. (Imagine being pulled 20 feet down into the water, then getting a leg and the opposite hand ripped off by a shark, struggling to get to get back to the surface for that breath of air you are about to miss). Graphic maybe, sorry, haha, but you get the idea.
Plus its much safer for your fish to avoid wildcaught food. That mouse could be eating a chemical concoction anywhere in your house or neighboors or anything.
If you really need to try something life, get a small mouse, like a pinky or a hopper, that is a 1 hit-KO on the mouse if the fish nails it.
Cheers,
Chris