Sure, you can hire the fish pathology expert (or send samples out to a lab), but our facility requires us to have "clean" fish coming in, so we can't do the exe

Sure, you can hire the fish pathology expert (or send samples out to a lab), but our facility requires us to have "clean" fish coming in, so we can't do the exercise of breeding, treating, and certifying fish in our own facility. The same is true of mice and rats. We have many pathologists on staff who could certify such a thing, but it would require setting up a "dirty" facility completely separate from the "clean" ones (complete with a separate animal care staff to change cages and such). Overall, the price is justifiable to avoid the trouble. You wouldn't even need a different specie to bypass the money-grabbing, you only need a new facility, your own certified processes, and some clout in the industry (read citations). Hell, you could start with the fish from the expensive vendor and sell the offspring (I think, unless there's a licensing agreement involved).