First, the oxygen consumption was determined of the sea anemones together with the clownfish. Then the anemones and fish were separated, and oxygen consumption was again measured for each. When together, the fish and anemones consumed 1.4 times more oxygen than when apart. In the next experiment, oxygen consumption was again determined while the fish and anemones were still separated but could see each other. The oxygen consumption remained lower. Apparently, physical contact was essential.
Observation with the aid of cameras revealed what happened when the clownfish was with the sea anemone: at night, the clownfish was very active and lively. The fins often moved vigorously and the fish dove deep into the anemone, which was forced to open up a little. And this is how the little fish provided the anemone with extra oxygen. The fish is apparently very effective: merely increasing the water flow over the sea anemone did increase its oxygen consumption mildly, but not as much as the clownfish could.