turns out ike jime (the mystical japanese fish-killing technique) yields better-tasting, better-textured fish by acclamation. the folks at cooking issues (now officially my favourite blog) proceeded to do some nifty investigative research on why this might be the case. the plausible explanation is that inserting the needle up the spine destroys the fish's spinal cord:
Certain fish that swim for very long periods have highly a highly developed autonomic nervous system for swimming (sounds like the CPG’s Bob was talking about). These fish, like bass, like horse mackerel, etc. benefit from spinal cord destruction. Other fish, like plaice, that don’t have highly evolved constant swimming reflexes, don’t benefit (or at least not as much). The paper recommends doing a species by species test to see which fish benefit the most. The paper didn’t mention CPG’s (in fact no paper did that I could find). Someone needs to do some research on that. So then, when you destroy the spinal cord, you destroy the swim reflex, which helps reduce ATP loss, delaying and softening rigor, increasing the quality of the fish.
this definitely did not emerge when i was talking to the professors at the tsuji academy about their fish preparation techniques in 2005.