There are a whole bunch of problems to overcome before a fisherman can sell well cared for fish to people willing to pay for that level of care. One problem is that federally licensed commercial fishermen MUST sell their catch to federally licensed dealers. Therefore, people who are seeking superior product have to find a dealer who handles such product. Second is the NYC model for distributing seafood, almost all of the seafood sold in NY goes through the Fulton Market, where there are few, if any, dealers that cater to this limited segment. It's better in some other areas like MA, where most of the dealers will differentiate line caught groundfish from net caught ground fish. But it is gradually improving, as some of the dealers are seeing increased margins on these more carefully handled fish. Of course I'm talking about our more common species, like Fluke, flounder, scup and sea bass. Tuna has been subject to specialized handling requirements for donkey's years, no tuna buyer will buy mishandled fish. IMHO its just a question of time, money and demand, before some of the more enterprising dealers start to step in to feed this demand.
Having said that, it is my experience that, as a general matter, commercial fishermen treat their catch much better than the average recreational fisherman. A couple of examples; a commercial fisherman would never put a fluke on the ice, white side down, while most recreational fishermen just throw them into the coolers; commercial fishermen use flake ice, which keep the fish much colder than ice cubes, or blocks, or ice in milk containers. Cod fishermen will eviscerate their catch ASAP after it comes on board, recreational fishermen will rarely do that. There are lots of other examples.