Personally, I fillet them.
What evidence do we have, though, that fish suffer? It’s clearly wrong to drag you into the water and drown you, but fish have only small brains, and don’t seem to demonstrate behaviors more complex than those of insects. It’s still a bad idea to torture them for torture’s sake - if nothing else, sadism’s a nasty habit - but it seems unlikely that killing fish increases suffering in the world to any appreciable extent.
I’ll just gut them (if anything) — most states require the head and tail be left on until you get home so length can be determined.
I’ve had catfish still alive after an hours or more drive home and several knocks about the head and other places. I know people who swear by the old ice-pick through the head bit but I’ve had mixed results with it. Short of field-dressing the darn things can’t be killed.
Since we can’t really know if the fish is suffering, and there’s a small thing you can do to make sure to the best of your ability that it isn’t, why wouldn’t you do that?
Because the likelihood that the fish is suffering is so small as not to justify even that slight effort or reduction in the quality of the meat. Fish brains are so small, and their observable behavior so limited, that the onus really must be on those arguing fish can suffer to make that case. Absent evidence fish suffer, why act on the premise that they do?
What evidence do we have that anything suffers? We only know suffering in ourselves. And that we evolved from something. And that most of what we are was passed to us by the ancestors we evolved from.
I suppose it’s possible that suffering sprang full-blown into humans and does not exist in other animals, but it seems the burden of proof would lie with someone claiming that.
And saying fish are “too primitive” to feel it…you do remember we’ve said some human beings are too primitive to suffer significantly, right? (See: slavery, circumcision of infants, etc.)
Because we can? Because, probably unlike Mr. Fishie, we are both blessed and encumbered with the ability to empathize with other creatures? The fish certainly looks like it would much rather be back in the water. I’m not suggesting going far out of one’s way to humanely kill a fish quickly, just taking a simple action out of kindness.
sitchensis
This. Solid whack on the head, then bleed via the gill and/or cuts in the tail. (Don’t trim the tail, for reasons mentioned upthread. )
Some fish - sharks, rays - have to be bled right away or they won’t be fit for consumption. Saltwater fisherman often keep a club called a fish billy for this purpose.
So, does that straw man give a nice, satisfying “THWACK!” when you hit it? Just curious - it’s an inanimate object, so you should feel free to hit it as hard as you like. 
I don’t contend that no animals other than human beings suffer. Clearly, humans suffer, and so complex brains are capable of perceiving suffering. Most large vertebrates have fairly large brains and display complex behaviors; it’s reasonable to suppose they have a measure of consciousness too, and can suffer in a way analogous to that experiences by humans.
But the fact that some Very Unpleasant People made a name for themselves by arguing (wrongly) that some humans are too “primitive” to suffer is not a persuasive argument against my position: Some non-human animals lack the neurological hardware for conscious suffering. We probably agree that chimpanzees are capable of suffering. We probably also agree that slime molds and paramecia are not. Unless you believe that Every Living Thing can suffer (which raises a host of questions - how do plants perceive suffering?), we agree that there’s a line. On one side of it are organisms with the neurological wherewithal to consciously experience suffering in a way that ought properly to arouse our empathy as moral creatures. On the other side of that line are organisms with no meaningful capacity for conscious suffering; these don’t really require our empathy or moral consideration.
Lest you still think I’m a monster, I’ll post question to the biological sciences dopers: Which is more difficult to get past your university ethics folks? An experiment that proposes to inflict noxious stimuli upon a monkey, or one that proposes to inflict noxius stimuli upon insects?
The world is full of grey, folks - saying that the appearance of suffering always matters, regardless of the reality, seems inadequate.
A fish out of water certainly looks like it’s dying - because it is. And the failure mode for fish in that state involves random movements. But the fact that you’d be in pain and frightened under those circumstances, with your enormously powerful brain, isn’t compelling evidence that Mr. Fishie is even slightly aware of his plight. And if there’s no one home in Mr. Fishie’s head, then you can’t show him “kindness” any more than you could a potted plant.
Did anyone ever truly make that argument? I don’t think the slavery advocates really honestly believed that the slaves couldn’t suffer. I think they knew damn well that they could, and just didn’t care. Back then, there was just a lot more suffering in general; people did backbreaking work all day long, all week long, all their lives. The people at the top just figured, “better them than me.”
This sounds like a conflation of the experience of suffering with consciousness of suffering. I don’t think there needs to be anyone “home” in order for suffering to take place. Pain is, whether the sufferer is aware of anything or not. Aware victims might be said to suffer differently or in more ways, though I could also see an argument in some contexts that the capacity for an awareness of the imminence pain’s end (even through death) might provide a relief unavailable to animals who can only live in the now.
(that’s from Consider the Lobster.)
I don’t think the point is really that everybody who fishes is Hitler. I think the point is, how are we so sure the fish doesn’t know enough to suffer? I mean, sure, if it really doesn’t, then it’s all just appearances - the worm that doesn’t appear to care whether you cut it in half or not is the example from the essay. But do fish? I don’t know at what level of sophistication I’m prepared to acknowledge suffering, but it’s definitely somewhere below human. I don’t know what the GQ answer is, but since your GQ answer appears to be that fish are below that threshold, I guess I’d like to know how you know.
a) knife thru the gullet to the gills to bleed them
b) ice them down in the live well/cooler - this is my usual method - makes them easier to filet as well.
Fish don’t ‘suffer’ - thats a human emotion - fish don’t have the brain system to ‘suffer’ - they may react, they may even feel ‘pain’ to some degree, but they do not have the nervous system to process it as anything other than as stimuli - there are countless studies on this out there.
The fact is, you don’t know if the fish suffers in a meaningful way, and you could do something simple to ensure to the best of your ability that it doesn’t. Why not? Why wouldn’t you take a few moments to show a kindness to another creature? Clearly, as said before, the animal is making its preference clear - it would rather not suffocate.
This leaves behind the yummy shoulder meat. Slice back from the front of skull to the gills, and then down.
Wife got her first marriage proposal from how she fried crappie. She was an early developer, dressed in a swim suit, and she had to tell the guy she was 15. He wouldn’t wait. A shore lunch can be good, but not worth waiting for.
I usually just leave any caught fish (that I’m keeping) on a stringer in the water until I’m ready to pack it up. Then I throw them into a cooler with ice. By the time I’m home they’re all dead. Except for maybe the catfish. Those you’ll have to cut off their heads before gutting them. Those critters are awfully sturdy.
a being’s rights are founded not by its capacity to suffer but by its capacity to reason.
We’re not talking about the being’s rights, we’re talking about the human’s empathy.
ETA - in other words, I would have a perfect right to cut my dog’s throat right now as he lays his head on my knee. However, I have a responsibility (as well as an emotional attachment) to him.
+1 on this. Cooking Issues has done extensive investigation of Ike Jime vs Western Bleeding techniques: http://www.cookingissues.com/category/ike-jime/ and found Ike Jime to make a measurable difference in the quality of the flesh.