But i think they really need those anemones to survive in the ocean, anemones can help them kill small fishes for them to eat and protect them from predators.
This is actually a true statement when they are in the ocean. However, in our tanks, they do not need one mainly because the fear of predator's is gone. They actually live quite a long life in an aquarium without the anemone as a host. There are more and more advances these days in getting more species to spawn in captivity.
The Percula Clown, is the main one to breed in captivity. These fish although their great, great, grandfathers swam amongst the anemone, the newborn's in captivity have never seen an anemone, and therefore have been bread out of the cycle, and do not require the protection of the anemone.
The reason most owners of clown fish have anemones, is to see these amazing creatures in action just like they would be in the wild.