Fish don't have nervous systems.
Someone told me that the other night. I wasn't sure. I did some research. There appears to be hard science behind it.
So it may be approaching literal truth that, as the rock star said, it's okay to eat fish because they don't have any feelings.
On the other hand.
In the 19th century, certain men of science claimed that dogs did not feel pain. What appeared to be responses to pain (whimpering, crying, struggling while being beaten or punctured) were mechanical reactions of an organism that was simply wired to avoid damage or destruction to itself.
So they would nail conscious dogs to tables and operate on them in surgical theaters.
The struggling and crying, they explained, was purely mechanical.
Dogs aren't fish, of course.
There is, of course, the dogfish, though.
I would eat the dogfish on a bed of rice.