Chaetodon nippon, also known as the Japanese butterflyfish, is a species of butterflyfish found in the northwest Pacific Ocean in the shallow seas around Japan, South Korea, the Philippines, and Taiwan. This striking fish has several interesting features:
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Description: The Japanese butterflyfish is a deep-bodied, vertically flattened fish that can grow up to 15 cm (6 inches) in length. Its dorsal fin has 12 or 13 spines and 18 to 20 soft rays, while the anal fin has 3 spines and 15 or 16 soft rays. The body coloration is creamy-brown, rimmed with dark brown. Juvenile fish have an eyespots near the region of their soft dorsal fin, which fades as they grow.
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Distribution and Habitat: This species is native to the northwestern Pacific Ocean, occurring in the waters of Japan, South Korea, the Philippines, and Taiwan. It is particularly common around the Izu Islands. The Japanese butterflyfish prefers rocky coastal reef habitats and has been recorded at depths of 5 to 20 meters (16 to 66 feet), although it likely inhabits deeper waters as well.
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Ecology: The Japanese butterflyfish is benthic and has an omnivorous diet, including polychaete worms, crabs, and other small invertebrates. It often moves in large or small groups. Interestingly, this species has been observed spawning in pairs. Its larval development has been studied, revealing that the larvae float upside down near the surface initially and then transform into juvenile fish with rapid color changes.
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Conservation Status: Despite being a common species, particularly in the Izu Islands, the Japanese butterflyfish seldom appears in the aquarium trade. Its population seems stable, leading the International Union for Conservation of Nature to assess its conservation status as "least concern".
So next time you’re exploring the reefs of the northwest Pacific, keep an eye out for the elegant Chaetodon nippon!
