What are you talking about LOL, thats only if you start inbreeding fish from the same parents continuously. How would culling be purifying a strain of defects, unless you're saying the whole population of a species is infected with a defect or disease which doesn't make any sense at all

...Usually, for an already endangered species, the point is to PREVENT hybrids and to maximize the numbers of pure specimens, not to start making all these hybrids to so called "strengthen the genetic make up." Your so called strengthened genetic make up has a very high possibility of being all screwed up because you're trying to combine two different species with two different genetic make ups. Theres a reason why so many hybrids have shorter life spans or come out sterile...