Spotfin Butterflyfish, Chaetodon ocellatus
Spotfin Butterflyfish, Chaetodon ocellatus. Underwater photographs taken in coastal waters of Yal-Ku, Quintana Roo, April 2017. Photographs courtesy of Juan Rojo, Akumal. As they are uncommon, deeper water residents and elusive they are a difficult underwater photograph-graphic subject. Both fish photographed above lack the black spot on the soft dorsal for which they are named.
Spotfin Butterflyfish, Chaetodon ocellatus. Underwater photograph taken in coastal waters of Bonaire, December 2019. Photograph courtesy of Bob Hillis, Ivins, Utah.
The Spotfin Butterflyfish, Chaetodon ocellatus, is a member of the Butterflyfish or Chaetodontidae Family, and is known in Mexico as mariposa perla amarilla. The Butterflyfishes are reef fishes and some of the most colorful tropical fishes in the ocean. Globally there are ninety-three species of Butterflyfish of which ninety-two are found in the genus Chaetodon, of which five are found in Mexican waters, four in the Atlantic and one in the Pacific Ocean.
The Spotfin Butterflyfish body has a strongly compressed oval disc. The adults are white with a black bar from the nape to a crest through the eye. They have a black spot at the top rear corner of the dorsal fin. The anal fin and dorsal fins are yellow with submarginal blue bands; the caudal fin and pelvic fins are yellow. They have a black spot at the top rear corner of the dorsal fin. The juveniles are similarly in color as the adults except they have an additional black bar that runs from the dorsal fin base to the anal fin. The fish undergoes a dramatic change of color at night with dark bands appearing on the body. The head has a concave upper profile, with a short, pointed snout with a small mouth equipped with long slender teeth set in bands of 6 to 9 rows on each jaw. The rear margins of the anal and dorsal fins are bluntly angular; and, the caudal fin is rounded. Their anal fin has 3 spines and 16 or 17 rays with the second spine being longer than the third; and, their dorsal fin has 12 or 13 spines and 18 to 20 rays. They are covered with rough scales. Their lateral line is incomplete.
The Spotfin Butterflyfish is found in small groups of 4 or 5 individuals over sandy bottom and in and around shallow reefs while feeding at depths up to 69 m (225 feet). The juveniles are found closer to shore within seagrass beds. They are the largest of the butterflyfish reaching a maximum of 20 cm (7.9 inches) in length. They are a diurnal species that feed on algae and benthic invertebrates during daylight hours. At night they hide trying to avoid predation by moray eels, various sharks and larger fishes. They are strong swimmers capable of maneuvering through coral reefs with ease by swimming sideways or upside down. Reproduction is oviparous in monogamous pairs that mate for life that become highly territorial. Each female releases small pelagic eggs with the pelagic larvae hatching within a day that travel great distances in the oceanic currents. The vast majority of young fish are consumed by other shallow water predators. The Spotfin Butterflyfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Spotfin Butterflyfish is a resident of all Mexican waters of the Atlantic including the Gulf of Mexico and the Caribbean but they are uncommon and very difficult to photograph.
The Spotfin Butterflyfish is similar in body profile to the eight other butterflyfish found in Mexican waters but it is a straightforward identification due to its markings taking note that the Reef Butterflyfish, Chaetodon sedentarius, is very similar but has a black stripe through its tail base.
From a conservation perspective the Spotfin Butterflyfish is currently considered to be of Least Concern with stable widely distributed populations. The major concern at present for their long-term survival relates to habitat degradation and loss of the coral reefs in which they reside. The Spotfin Butterflyfish is a popular aquarium item due to its beauty and hardiness and sold commercially for the aquarium trade. They present a challenge to divers being uncommon and found in deeper waters and they retreat rapidly from encounters.