Maybe some. But we have known about inbreeding for a long time. When Charles Darwin's daughter passed away, he felt guilty because he thought it was because he married his cousin (don't think it was a genetic illness though).. That was back in the 1800's... Ancient dog breeds also are less prone to genetic illness, a lot of those breeds that weren't created just to make a breed, but bred as working animals over centuries, as opposed to something like Dobes, which were pretty much created over one guys life time. If you look at serious labradoodle breeders today, you are right, they are much more careful with what they're doing.
Taking it back to fish... You can't really know, we don't register fish, most people don't track their lines, etc.. To think something like a balloon fish can be produced in just a few generations is atrocious. Betta breeders cross fish so much that it hurts.. Schooling fish are left to breed with who they want, they are hard to track.
And then, even the weakest survive. I read an article on PFK about how cichlids, once vicious monsters, are turning into timid fish. In the wild only the aggressive ones survive, but in our tanks pretty much everyone can. If that's counter productive to these fish isn't really clear to me. That seems more like backwards evolution.
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