Originally Posted by foodguy
well, a couple of things. first: like any other animal, fish need to go through rigor mortis to taste their best. the whole live tank thing can be treacherous for the beginning cook. just-killed fish need to be cooked very gently (steaming, poaching), or they toughen and are flavorless.
also, often the freshest-tasting fish you can find is frozen. fish that has been carefully handled, quickly and carefully frozen, and then defrosted carefully is as good as fresh-caught any day.
What do you know about the ike jime method? Have you read/written anything about it? Supposedly what happens in fish is that the ATP in their muscles (what makes muscles contract and relax) runs out, and the muscle has no more ability to relax itself. So what happens is that each time the fish contracts, the muscle is then set in place, since the compound allowing it to relax is no longer there. So the faster and harder that the rigor sets in, the lower the quality of the final product. Ike Jime is a slaughtering method where they make a small cut behind the brain and a small cut along the tail, and then slip a needle into the spinal cord to push all the spinal fluid out. The fish is then chilled in ice water and allowed to bleed out. By destroying the spinal cord, you affect how much ATP is lost, which means rigor sets in less hard and less fast, and it results in a higher quality filet.
Personally, I don't know about all the science behind it obviously, I'm a cook, not a scientist. But I have seen fish killed ike jime style before, and I've eaten fish that were killed at the same time ike jime method and regular method, and the difference is vast and really goddamn impressive. It is almost insane how much it effects the quality of the fish. IIRC, some blog did a big post about it. I remember reading it somewhere, but don't remember where. But then at my last place of work the fish supplier did an ike jime demonstration and it blew my mind.