Are we actually much more cruel to fish than to other animals that we slaughter?

We suffocate them to kill them when we pull them from the sea. That's quite mean. Few people would advocate the humanity of killing a cow in the same way.

Are you aware of how cows are actually killed?

Fair enough. How much more would it cost / how much more would one have to pay for humanely slaughtered tuna and salmon, I wonder? Would there be a market? After all, we have certified-organic, fair trade, halal and kosher....

Or freeze them live into a block of ice.