You Have Ocellaris Clownfish so they don't claim a huge area if you observe them in the wild but for your tank they will claim an area about the size of your tank. They'll spend most of their time in one area, possibly a corner, but they will defend their area against intruders. An adult Clownfish is considered an intruder so they will leave their nest to chase off the intruder. They, especially the female, will continue to harass the intruder until it leaves.