In recent years, anemonefish (genus Amphiprion, family Pomacentridae) have emerged as a model system to study the behaviour, physiology, ecology and genomics of coral reef fishes. Laboratory rearing, once considered very difficult, is becoming more approachable, which in turn allows for laboratory and in-situ experiments. Using information attained from both these sources, the goal of this chapter is to address the main characteristics of anemonefish reproductive behaviour by answering questions about who, how, where, when, how many and why reproduction varies.

Who? Anemonefishes are group-living protandrous sequential hermaphrodites with a single mating pair per anemone and a variable number of non-mating individuals. Hormone levels (in particular 11-ketotestosterone) provide a good proxy for male sex, aggression, and sexual activity in clownfishes. How? We discuss spermatogenesis, oogenesis, and the ovotestis which is a unique feature of these sex-changing species. In addition, reproductive behaviour pre-spawning, during spawning and territoriality, as well as egg development and hatching are described. Where? Anemonefishes associate with ten species of host anemones. When? Anemonefishes spawning at different temporal scales are described, including daily to yearly patterns. How many? Until recently, actual fecundity was very difficult to measure within appropriate time scales. In this chapter, actual fecundity, including early egg mortality, is described from field experiments. Where they spawn, how they spawn, whether they spawn, and how many eggs they spawn are all affected by human activities. In that respect, anemonefishes are the sentinels that warn us of the ever-increasing disturbances affecting coral reefs.