I truly believe that anglers have trained them over the years. Every fish that is brought to the surface is subject to being attacked and cut in half by the six and eight foot long “logs” under the boat. I believe they realize that a boat sitting in the water means an easy meal will soon follow. It appears to be some sort of learned response.
On the other side of the ledger, the remora, which normally attach themselves to some large fish, usually sharks, were attaching themselves to our boat bottom. Every bait we sent to the bottom was followed down by at least one remora. And, it didn’t seem to matter where we fished. They were everywhere.
We caught several remoras, and to prevent them from being harmed, we cut the leader and left the hook in them when we saw that they were hooked deep. They were released, none the worse for wear. Those hooks would dissolve in a few days.
I began noticing after a while that most if not all the remoras under our boat had a monofilament leader hanging out of their mouth. They swam freely and still actively pursued our baits as we fished. Here is a fish – supposedly in pain – acting as if nothing ever happened.
When I catch a grouper, there are invariably marks inside and on the roof of its mouth: fish fins from a recent meal, and yes, even an outline of a fishhook. Fish are carnivorous. They eat each other. Fish also have protection in the form of fins – fins that protrude to give the perception of size. I would think that if another fish’s fins caused pain in a feeding fish' mouth, that feeding fish would turn into a vegan after a while.
When any fish eats another fish, fins and holes from fins are a necessary part of life. So, as I see it, a fishhook is in the same category. It is no more than another hole that does not bother a fish, and that heals over quickly.