the guy in that thread who said he talked to his vet is full of crap (or maybe his vet is). directly from the AVMA website, under the special considerations heading AMPHIBIANS, FISH, AND REPTILES-- "use of clove oil is not acceptable" followed by "euthanization by cooling of REPTILES is inhumane, EVEN IF combined with physical or chemical methods" At no time does it deal with fish, particularly warm water marine species.In fact, the only openly endorsed methods mentioned are decapitation (followed by pithing), or injection (and the injections are $$$, according to my sister, a vet)
I use freezing (as I have said before), after conversations with several PhD's of marine biology, and a vet (my sister, as mentioned above). according to them, the enzmes used in metabolism in tropical marine fish basically cease to function at about 50 degrees. Also, while there is evidence that fish feel discomfort, that can't be equated to feeling pain the same way we do.
Also, the guy that claims that most sharks are warm blooded is wrong. some sharks, while still basically ectothermic, can slightly raise their body temps above that of the surrounding water for short periods of time (Great Whites and Makos use this to give them bursts of speed for hunting, for example)