About Chaetodon lunulatus Quoy & Gaimard, 1825
Chaetodon lunulatus, commonly called the oval butterflyfish, has similar coloration to the blacktail butterflyfish (C. austriacus) and the melon butterflyfish (C. trifasciatus). The blacktail butterflyfish has black caudal and anal fins, while the melon butterflyfish is an Indian Ocean species that has a more conspicuous dark patch below its dorsal fin and a mostly yellow anal fin. Chaetodon lunulatus can reach a maximum length of 14 cm. It has approximately 13 to 14 dorsal spines, 20 to 22 dorsal soft rays, three anal spines, and 18 to 21 anal soft rays. Along with the blacktail and melon butterflyfishes, and likely the unusual Arabian butterflyfish (C. melapterus), C. lunulatus forms the subgenus Corallochaetodon. This subgenus is probably closely related to the subgenus "Citharoedus" — a name that is a junior homonym of a mollusc genus — which contains the scrawled butterflyfish (C. meyeri). If the genus Chaetodon is ever split into separate genera, the Corallochaetodon group would likely be separated into the genus Megaprotodon, along with the Citharoedus group. The oval butterflyfish is distributed across the Pacific Ocean, ranging north to Japan, south to Australia, and east to Hawaii and the Tuamotu Islands. It is a benthopelagic tropical species that inhabits coral reefs, found at depths between 3 and 30 meters in coral-rich lagoons and semi-protected seaward reefs. Small juvenile oval butterflyfish are secretive and hide within corals. The oval butterflyfish is oviparous and shows very little sexual dimorphism. Individuals of this species may live either solitarily or in pairs. Research shows that most pairs are heterosexual, an arrangement that most likely developed to ease reproduction. Partner fidelity is often long-term; one study recorded pairs staying together for up to seven years. In established pairs, females feed more often, while males tend to lead when the pair swims in tandem. Pairs regularly swim parallel to each other in close proximity, usually staying within 1.5 meters of each other, and almost never move more than 4 meters apart.
