JC,
One thing that is good about releasing Cod (as opposed to Stripers, or Trout, Bass, Etc.)is that if you have NOT done it right, you will know right away. They either swim away, or they don't. The "venting" that you talk about is not necessary. If you have one that won't release, there may be some value in attempting to vent the fish. I have been successful before in "burping" a Cod that would not swim. The "shock" that I mentioned before (Gills turning pink) is your biggest enemy in releasing a Cod though. Of course as with other fish, I am sure there is some mortality problems even with the ones that do swim away. But that happens with all species of fish that are caught and released. As far as the Fluke thing goes.... you are absolutely right. There should at least be a slot limit on them. If your intent is to improve a fish population, It does not make a lot of sense to me to let 15" fish go, and then kill 20" fish. We certainly have some real genius's making the rules, don't we.....