OBSERVATIONS ON THE SYMBIOSIS OF THE SEA ANEMONE STOICHACTIS AND THE POMACENTRID FISH, AMPHIPRION PERCULA

Abstract

1. The behavioral process is described whereby the fish Amphiprion percula, after long isolation from the anemone Stoichactis, effects its association with the host.2. This process appears to involve a gradual acclimation to the host, brought about by increasing contact with the host's tentacles. This appears to effect the establishment of both the "bond" and the physiological protective barrier between the animals.3. Evidence is presented that an active principle is present in the mucus secreted on the outer surface of the integument of Amphiprion which raises the threshold of mechanically-induced discharge of the host's nematocysts. This factor does not affect the threshold of electrically-induced discharge. It is fast-acting, specific in its effect and heat-labile. It is not present in the muscle of the fish.4. After contact between the host and an acclimated commensal no feeding reactions can be observed in the anemone such as occur when similar contact is made between Stoichactis and prey fish or between other anemones and Amphiprion. It is possible that this "inhibition" of the anemone may be the result of a direct effect on the nervous system by the active principle. However, it would seem more probable that this absence of feeding reactions even on violent contact may depend upon the fact that nematocysts are not discharged. Perhaps stimuli from receptors in the tentacles sensitive to nematocyst discharge or to substances from "stung" prey are necessary for the initiation of feeding reactions.