As mentioned earlier, gigantea and magnifica are the natural hosts of ocellaris (and perculas, for that matter). And, providing a healthy host even captive bred clownfish usually waste no time being hosted. Research studies suggest that it has to do with chemicals shed by the anemone that the fish essentially smells and knows where to find the anemone. In nature, as soon as the baby clownfish goes from larval stage to baby fry stage it must find an anemone or be eaten. Clownfish are never found living sans anemone in nature. Therefore, it's essential clownfish immediately upon metamorphosis from larval stage find a host. That instinct has not been bred out of clownfish through repeated breeding in captivity without an anemone. I personally have never seen a natural host anemone be rejected by a natural clownfish symbiont species. I've heard people say that's happened, but I think it's safe to say it's practically nonexistent. I've always had captive bred clowns, provided the natural host (because I'm specifically interested in seeing the natural interaction between clowns/anemones as in nature), and the fish go to the anemone pronto. With the species of clowns you have, unfortunately magnifica/gigantea have a much lower survival rates compared to BTAs. Mags/gigantea are quite tough after they acclimate to a tank, but very often they die within weeks after being added to the tank, presumably due to the shipping process compromising their natural immune defenses--with the anemone sadly succumbing to bacterial infections.
