Do fish feel pain?

[The Grand Nudger]

I am not sure this precautionary principle ("In case you are not certain whether something is sentient, treat it as if it is.") works well in politics. Sure, it works in ethics as a way to make the debates about solipsism irrelevant to ethics, but I am not so sure it works in politics. When we say "Fish should be treated as if they felt pain.", we are advocating for coercion. We are saying that fishing ships should somehow be modified to kill the fish humanely, which costs money and, in all likelihood, freedom (as fishers probably need to be forced to do that). One who is advocating for coercion has the burden of proof, doesn't he?
Sure, sometimes coercion is justified, such as regulating the use of antibiotics in the egg industry (as it's basic biology that it causes superbacteria). But coercing people to kill fish humanely even though we aren't certain they feel pain... I am not sure that's justified.

Good thing I'm not looking to make my precautionary principles into laws, then, eh?  

I'm of the opinion that the best way to get producers onboard with humane protocols isn't to try to coerce them...either personally or with legislation.  It's to show them how to use those protocols to increase their profit.  In my experience that's worked a whole lot better than any amount of concerned lectures or debates about whether the livestock feel pain. That's only half the struggle, too. Then you have to get the producer and the consumer to interact more closely...because even though the consumer for a niche product is already convince about the thing, they're rarely aware of or initially convinced about the price.