Sunset butterflyfish

Geographical Origin and Habitat: Chaetodon pelewensis is native to the tropical waters of the Central and Western Pacific. Its range includes the islands of Palau, the Great Barrier Reef, Fiji, Samoa, and French Polynesia. It primarily inhabits outer reef slopes, shallow lagoons, and areas rich in hard corals at depths ranging from 1 to 30 meters. It is often found in areas with moderate to strong currents, where branching corals grow.

Taxonomy and Morphology: Belonging to the family Chaetodontidae, genus Chaetodon. It has a disc-like, laterally compressed body with a pointed frontal profile and a small terminal mouth. Adults reach a maximum length of about 12-13 centimeters, making them one of the smaller butterflyfish species. It features small brush-like teeth suitable for picking food from rocks and corals.

Social Behavior: It is an active and curious species. In the wild, it lives solitarily or in stable pairs. It exhibits strictly diurnal habits, constantly patrolling the coral reef in search of food. In the aquarium, it may show moderate territoriality toward conspecifics or other butterflyfishes with similar coloration, while generally ignoring other species.

Coloration and Sexual Dimorphism: The base coloration is yellowish or silvery-white on the sides, shading into a deeper yellow on the back and belly. The body is crossed by a series of parallel dark diagonal lines running upward and backward. A vertical black band runs through the eye, and a dark patch is present on the caudal peduncle. There is no visible sexual dimorphism.

Aquarium Setup: Requires a mature marine aquarium of at least 250-300 liters (approx. 65-80 gallons) for a single specimen or a pair. The layout should include live rock structures rich in crevices and caves where the fish can hide when startled, while ensuring ample open space for swimming. A vigorous, well-oxygenated water flow is recommended.

Diet and Feeding: In the wild, it feeds on coral polyps and small benthic invertebrates. In the aquarium, although it is a partial corallivore, it is more inclined to accept commercial foods compared to other Chaetodon species. The diet must include mysis, brine shrimp, chopped krill, clam meat, and algae-based preparations, distributed in multiple daily portions.

Water Quality: Demands stable and excellent parameters: temperature 24-27°C (75-81°F), pH 8.1-8.4, specific gravity 1.021-1.025, and nitrates below 15 mg/l. An efficient protein skimmer and regular partial water changes (10-15% every two weeks) are necessary to keep the organic load low.

Compatibility and Cohabitation: Coexists with peaceful fish such as wrasses, gobies, and clownfish. It is not reef-safe: it will inevitably nip at the polyps of stony corals (SPS and LPS) and clam mantles, so keeping it in reef tanks with prized corals is discouraged. It can be housed in fish-only tanks with live rock.

Aquarium Breeding: Breeding in captivity is not documented in the commercial trade. They practice pelagic spawning in pairs, releasing buoyant eggs into the water column. Larval development involves a planktonic phase and feeding with microscopic live zooplankton, which is highly complex to manage.

Risks and Diseases: It is sensitive to skin parasitic diseases such as Oodinium and Cryptocaryon irritans under transport stress or sudden temperature changes. A careful quarantine before introduction is recommended. Providing a rich and varied diet is essential to stimulate appetite and prevent starvation.