Sea anemones and anemonefish: A match made in Heaven

Sea anemones are amongst the most venomous organisms on earth and yet there are species of fish and crustacea that are known to tolerate anemone venoms and live in association with them in a mutually beneficial relationship. One of natures most compelling displays of symbiotic behavior is found in the relationship between anemonefish and their sea anemone host. This relationship was first described more than a century ago and despite it being widely studied since, our understanding of the evolution of the relationship and the mechanisms and behaviors involved remains shrouded in mystery. Anemonefish (Family: Pomacentridae) comprise of a distinct group of 28 species that are able to live within sea anemones. Despite the large diversity of anemones in the tropics, only ten species are suitable as hosts for anemonefish. Within these species, only certain pairs of anemone and anemonefish are compatible and found in the wild together. This relationship is obligatory for the fish and in some cases for the anemone, meaning that the symbionts are entirely or heavily dependent on each other for survival. Symbioses between the two groups provide the following benefits: mutual protection from predators, an exchange of nutrients, improved reproductive and lifetime fitness. While past studies have explored the different patterns of host species that fish use and multiple authors have examined the mechanisms involved in protecting fish from anemone venom, how fish acquire immunity from the anemone’s stinging tentacles and why only certain anemone species are found associated with some anemonefish more often than others still remains uncertain.