well, when I said bacteria free, it's not 100% free of all bacteria...what I mean is that since they are not born in natural ocean and the harboring environment (the fish tank) is already free of most diseases, like white spot, fungi....so when customers buy them, such kind of Nemo can simply adapt the new (or change) temperature, and no need to "experience" the quarantine procedure which is a touture to marine fish coz the first thing first of quanantine procedure is putting the marine fish in fresh water, you can imagine how the fish feels...
So, I dream some days later if the scientists can discover how to breed all marine fishes in lab / artificial environment, then keeping marine aquarium would be really simple & care-free... at the moment, certain corals (particular hard coral) can asexually propagated already...