SOCIALLY CONTROLLED GROWTH AND SIZE-DEPENDENT SEX-CHANGE IN THE ANEMONEFISH AMPHIPRION-FRENATUS IN OKINAWA, JAPAN

Social structure, growth and reproductive experience of a protandrous anemonefish, Amphiprion frenatus, were investigated on a coral reef in Okinawa, Japan. In a 67 m x 334 m study area, 24 breeding groups, 10 nonbreeding groups and 2 groups of unknown breeding experience were found around isolated sea anemones. One group usually consisted of 2 or 3 fish. The female in a breeding group was larger than not only her mate but also all males in other breeding groups. The body size and gonadal state of the largest individual in a nonbreeding group were intermediate between the female and male in a breeding group. In both breeding and nonbreeding groups, the largest fish retarded growth of the second largest. After the disappearance or removal of females, their mates took more than 1.5 years to attain the minimum functional female size (about 75 mm in standard length). This delayed sex change can be attributed to strong growth suppression by the female.