“Selective breeding is the opposite of natural hybridization.”
No it is not. It is exactly the same thing. Hybridization is how you selectively breed. It is just physical manipulation of something that nature will allow. Nature allows manipulation of pollen swapping and selecting the best of seeds and pollen from the best of plants. Nature will allow grafting of similar species from one to the other. Or interbreeding animals of a different shape, color, or size.
Putting fish DNA in a plant is not going to be allowed naturally anymore than crossing a cat with a dog. Or a duck with a fish. GMO can force those unnatural combinations. If nature will not allow it then it is unnatural.
NATURAL hybridization (which are the words YOU USED) is what happens NATURALLY when plants and animals adapt for local conditions. Selective breeding is what happens when PEOPLE look at these naturally hybridized plants and say “this one here produces more fruit, but it doesn’t taste good; that one over there makes very little fruit, but it tastes great; what happens if we find a way to get them to breed”. And sometimes it works and you get more better fruit. But also often you wind up with something like corn that can no longer propagate itself and would cease to exist without us. NATURAL hybridization will never result in a plant or animal that can’t propagate itself.
Putting fish DNA in a plant is just the new high tech way to wind up with a plant that does what we want it to rather than what nature wants it to. But at it’s core it’s no different than making corn.