Chaetodon mertensii

Common Names: Atoll Butterfly Fish
Eastern Pearlscale Butterfly Fish
Family: Chaetodontidae
Category: Chaetodontids
Distribution: Pacific - Eastern; Ryukyu Islands, south to the Philippines, Lord Howe Island, Tuamoto and Marshall Islands. Aslo found around Rapa Nui (Easter Island).
Main Ecosystem: Reef; Inhabitant of mature reefs with established populations of stony reef building corals such as Acropora species.
Temperament: Peaceful; Likely to be territorial with conspecifics (except in the case of mated pairs) and also toward other Butterfly Fishes of similar appearance. Integration with Butterfly Fishes of dissimilar appearance possible in large aquaria, but best left to advanced aquarists. Compatible with a wide range of other fish species from other Families - these should be, like this fish, peaceful but active.
Diet: Carnivore; In the wild, this fish is a feeder upon live coral polyps from hard stony corals, assorted benthic invertbrates, filamentous algae and possibly macroalgae too. Consequently this fish is NOT REEF SAFE in an aquarium in which live corals are being cultivated, and is unlikely to be safe with Zoanthids and certain other sessile invertebrates too! Can be migrated to more practical aquarium foods, but this may prove challenging: Mysis Shrimp, Cyclop-eeze and other similar marine fish foods should be supplied, and filamentous algae should be present in the aquarium for it to graze upon. May also eat decorative Caulerpa!
Care: Provide spacious aquarium (75 gallons and up) furnished with branched coral skeletons to provide cover and shelter. A "medium difficulty" Butterfly Fish requiring scrupulous attention to water cleanliness if it is to prosper in the aquarium. Choose companion fish species that are active but peaceful.
25°C - 27°C
77°F - 81°F
Specific Gravity:
1.022 - 1.025
Potential Size: Male: 14cm (5.5")
Female: 14cm (5.5")
Water Region: Middle; In the wild, found close to large branched coral skeletons which provide protection and cover.
Activity: Diurnal; Active throughout daylight hours as a forager and algal grazer.
Gender: None known.
Breeding: Captive breeding unknown at present. Reportedly an open water egg scatterer in the wild, presumably with pelagic larvae, thus making aquarium cultivation of the young extremely difficult.
Variants: None known.
Comments: Differs from the very similar Chaetodon xanthurus in lacking a spot above and behind the facial eye stripe (a spot of this kind is also present in Chaetodon madagaskariensis). Differs from Cheaetodon paucifasciatus in that the posterior colour patches are orange, not red. The range of this fish is close to, but not overlapping with, Chaetodon xanthurus, and thus knowledge of the geographical point of origin of a specimen will confirm identity, particularly if collected from the distant Micronesian and Polynesian Islands.
Main Colours: White, Black, Orange
Markings: Striped And Spotted
Mouth: Normal
Tail: Flat
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Submitted By: Calilasseia
Contributors: Calilasseia
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