I was speaking with a friend today about the issue of animal rights and he re-articulated a cogent argument that I wanted to very briefly reproduce, and apply to the issue of fishing.
Harm is bad
Consider any concept of ethics you've heard proffered - from the Stoics to Rawls - and you will notice that the belief that "harm is bad" is either explicitly stated, is implied in the argument itself, or follows. Think about your own beliefs: Shouldn't suffering be limited; don't you accept the premise that pain, for example, should be reduced as a matter of ethics?
Now, to what principle can we appeal when attempting to defend the position that the harm suffered by certain groups doesn't matter ethically - or when we imply that while harm is bad, harm to some groups of people is worse than others? The answer is simple: prejudice. And it's not a defensible position.
The follow example is illuminating: from P.E.T.A. - 'Fishing Hurts'
Because no U.S. law regulates the treatment of fish, both commercial fishers and fish farms treat fish in ways that would warrant felony cruelty-to-animal charges if the victims were dogs or cats instead of fish.
Dragged from the ocean depths, fish undergo excruciating decompression - often the intense internal pressure ruptures their swimbladders, pops out their eyes, and pushes their stomachs through their mouths. Then they're tossed on board, where many slowly suffocate or are crushed to death. Others are still alive when their throats and bellies are cut open. Remarkably, fish farming is even worse because farmed fish are fed 5 pounds of commercially caught fish (species not eaten by humans) for every 1 pound of fish flesh produced.
Factory-farmed fish are subjected to extreme crowding and filthy conditions, which spread infections and parasites. Farmers use antibiotics and other drugs to keep the fish alive and to make them grow, but because the conditions on factory fish farms are so horrendous, up to 40 percent of farmed fish die even before slaughter.
Consider further the issue of "sport" fishing. As opposed to allowing an individual fish to suffocate to death, some people prefer to crush their skulls with a rock. Imagine that; failed attempts aside (although that's just disgusting to think about), consider the fear, distress and pain of that experience.
So, returning to this prejudice: What we say when we are eating animals is that our gastronomical interest - "Fish flesh tastes good" - ought to trump or at least count for more than the fish's fundamental interest in not being harmed (e.g, suffering, pain, death).
But why? Evidence supports the belief that fish can suffer in many of the same ways that I can - including psychologically; they can be harmed to the same degree and intensity, and yet, that doesn't matter to us.
This is a prejudice; it's similar in kind to racism, classism and sexism. Our defense of this prejudice is as base as bigotry: "They're not humans" - meaning, "They don't belong to our group, so their harm doesn't count."
How can we implicitly accept this premise while attempting to counter the arguments of the racist for example, who argues that blacks aren't a part of our group, therefore, their interests - no matter how fundamental - ought to be trumped by the interests of the group-members.
It's speciesism. It's as indefensible, ethically, as refusing women entrance into the community of those who matter because they don't have a penis.
Despite the fact that there is scientific evidence to support the assertions that fish do in fact, feel pain; most people do not believe this fact.
Peter Singer made a really excellent point in the book you lent me about whether or not fish feel pain. He wrote that fish should be given the benefit of the doubt in such a situation. Singer compared it to driving down the road at night and in the road ahead of you, you see a large object. You don't know if it's just a bag of clothes or an animal, but either way, you give the object the benefit of the doubt by swerving to avoid it. By swerving, you either avoid causing anymore pain to a living being or you just don't drive over an empty cardboard box. But in either case, the driver looses nothing and has everything to gain by not causing more harm.
Even though it has been proved otherwise, and intelligent and informed people know that fish do feel pain; all that aside, whether or not a creature is sentient should be given the benefit of the doubt and we should all assume the worst.
Singer's analogy is apt - I often make the same point with insects and shell fish. I simply argue that the evidence suggests that these creatures aren't sentient (which, as you say, is certainly NOT the case with fish); however, as I can exist without harming (assuming they can be harmed) these creatures intentionally, I make an assumption of sentience and act accordingly.