Remember Bubble Boy. If you have no immune system, you must live in a bubble or else the common cold will kill you. I think the argument is, stripping the fish's immune system then forcing them to live together in groups of fish who also have their immune system's stripped in hopes a random parasite or pathogen never makes it into the tank, is a ticking time-bomb.
What's the longest living fish that was quarantined at an early age?
What's the longest living fish that was quarantined at an early age?