Saddleback Clownfish

Fascinating facts about the Saddleback Clownfish

• A single saddleback clownfish can be found from a shallow lagoon at 2 m down to the reef’s edge at 30 m.
• Even though anemonefish usually show a big size gap between sexes, the male saddleback is almost as big as the female – a trait that lets him dart away from predators or race back to shelter in the sand-buried anemone.
• When a breeding female disappears, the next-largest male instantly flips gender, and the biggest non-breeder steps up as the new male, keeping the group’s hierarchy intact without any new fish joining.
• In the wild this clownfish only partners with two of the ten known host anemones – the rare Heteractis crispa and the more common Stichodactyla haddoni.

At a glance

About the Saddleback Clownfish

The saddleback clownfish, Amphiprion polymnus, is a striking black-and-white anemonefish that earns its name from a bold white saddle across its mid-body, flanked by two or three crisp white bars. Growing to about 13 cm (5.1 in), its stocky, laterally compressed form shimmers in shades from dark brown to yellow-orange, with an orange-yellow snout and pectoral fins. The white head bar sits just behind the eyes, while the caudal and anal fins are edged in white, creating a vivid contrast that makes the fish instantly recognizable in the silty lagoons and harbour areas of the Coral Triangle, from the Philippines through Indonesia and New Guinea to northern Australia, Melanesia and the Ryukyu Islands of southern Japan, at depths of 2–30 m (6.6–98.4 ft). A. polymnus lives in a tightly ordered social group anchored to a host sea anemone, either Heteractis crispa or Stichodactyla haddoni, where it finds shelter and a breeding site. The species is a sequential hermaphrodite: the largest individual is the female, the next largest the breeding male, and smaller males line the hierarchy. If the female dies, the breeding male transforms into a female and the biggest non-breeder steps up as the new male, a remarkable example of protandry. Diurnal and aggressively territorial, the fish feeds on zooplankton, tiny benthic crustaceans and algae, while also defending its anemone from reef fish such as butterflyfishes. A surprising trait is its ability to alter coloration within hours after switching host anemones, becoming lighter or darker depending on the new symbiotic partner.

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