Active provision of food to host sea anemones by anemonefish induces host growth

In mutualistic symbiosis, organisms often provide food to their partners, but the process and significance of food provisioning to the hosts remain poorly understood. Anemonefish Amphiprion clarkii, which prefers larger host, has been suggested to provide food to its host sea anemone. In this study, we investigated food provisioning by the anemonefish and its effects on the symbiotic relationship. When given foods of various sizes and types in the field, the anemonefish selectively consumed small animal food and seaweeds, while providing larger pieces of animal food to their hosts but avoiding inedible seaweeds. When repeatedly given small pieces of animal food, the anemonefish initially consumed the food themselves but later increased provisioning to the host. This food provisioning positively influenced the growth of the host anemone. These findings suggest that anemonefish actively provide food to host anemones based on the situation and may cultivate their hosts, resulting in mutual benefits.