This is how you humanely kill a fish and why you want to.

A thread.

I use a simple nail and the back of my hatchet. You want to stab the fish from the side through the skull into the brain ASAP after you reel it in.

This kills it instantly.

It is called "brain spiking".

When you only toss a live fish in ice not only does it flop around and bruise itself as it slowly suffocates, but the entire time it is dying it releases stress hormones. You can taste it when an animal dies painfully.

Brain spiking prevents both the bruising and hormones.

After that I ALWAYS bleed my fish. You don't want your meat marinating in blood... it'll make your meat go bad faster and be less tender.

To bleed your fish, the fastest way is to chop off the head and tail. Then rinse it. I use my hatchet.

The next time you go fishing, try these techniques. You can not only taste the difference, but if you compare the meat of a fish not brain spiked and bleed to the some same species caught same time/place, the brain spiked and bled fish will have whiter flakier more tender flesh.

Photo credit, "Cameron white"

There are more detailed ways to bleed your fish. This is the and easy way.