Protection from predatory reef fish is the primary fitness benefit anemones gain by acting as a host to anemonefish, as proposed by Allen and Fautin. Anemonefish gain protection by living within the stinging tentacles of anemones, and this mechanism as outlined above remains unsolved. The physiological costs involved in protection must exist, however, the advantages gained for the fish are a long lifespan and an increase in reproductive fitness. To maximize fitness, anemonefish should choose anemone hosts that ML406 provide them with the highest quality refuge at the lowest cost to themselves with respect to physiological expenditure. If anemone quality varies, competition should exist for highest quality hosts, and is indeed the case as reported by Fautin and others,. Clearly, the question of ��What defines a high quality anemone in the eyes of an anemonefish?�� must be explored. Anemone morphology does differ amongst the 10 host species, primarily in overall size and in tentacle length. Another characteristic that has clear variation is toxicity, and we believe this could be a critical factor in determining the quality as a host for anemonefish and may be responsible for limiting the number of anemone species, which can form a symbiotic relationship with anemonefish. Senc��ic�� and Mac��ek summarized the properties of venoms from fifteen PHTPP different anemone species, none of which acts as a host for anemonefish, and found a significant difference in their lethal potency. A more recent review of 32 anemones included one species that hosts anemonefish found that its venom was a group II peptide of relatively high potency. Understanding the relative potency of the toxins among the host anemones will provide key information necessary to determine how anemonefish develop tolerance to the venoms, which in turn will provide insight into the existence and maintenance of the symbiotic relationship and how this association may have evolved. Crude venom from nine anemone species that act as hosts for anemonefish showed significant differences in haemolytic and acute toxicity. Variation in relative neurotoxicity was also observed among anemone species.