News / Species Spotlight / Species Spotlight - Marquesas Butterflyfish (Chaetodon declivis) (08/30/17)

Species Spotlight - Marquesas Butterflyfish (Chaetodon declivis)

Species Spotlight - Marquesas Butterflyfish (Chaetodon declivis)
Roaops is a small genus of mesophotic butterflyfish, which has endeared itself to aquarists thanks to the robust nature of its species and their relatively benign behavior in reef tanks. Though exceptions arise, these fishes can usually be mixed safely with most corals, as the natural diet in this group tends more towards picking at benthic crustaceans and worms, as well as the occasional planktonic morsel.

A handful of regional populations make up the currently recognized species-level diversity here. Theres C. mitratus in the Indian Ocean, easily recognized thanks to its yellow hue. C. burgessi occurs across the West Pacific and into Micronesia. Hawaii is home to C. tinkeri, and a similar (and presumably undescribed) population exists far to the south in French Polynesia and the Cook Islands. And then there C. declivis, known as the Mauritian or Declivis Butterflyfish, which has separate populations in the Marquesas and Line Islands.

These two isolated archipelagos represent some of the easternmost segments of the larger Polynesian ecoregion, and both have a tendency for fostering endemic speciation. The question that has yet to be answered for C. declivis is whether or not these two regions are truly sharing a single species, or, more likely, if there are possibly two similar but separate populations. There are even separate subspecific names for these, with the true C. declivis hailing from the Marquesas, while C. declivis wilderi is described from Kiritimati.

This distinction is important to aquarists, as there is no fish collection allowed in the Marquesas, meaning that all captive specimens of this fish are actually of the wilderi variety, generally being sourced from Kiritimati (AKA Christmas Island, not to be confused with the Christmas Island found west of Indonesia). In essence, there is no true Marquesan Butterflyfish in the aquarium trade, just the highly similar population from the Line Islands. Its been suggested that there might be subtle color differences between the two with regards to the relative darkness of the scales and the yellowness of the back, but this has been increasingly argued against as more images have come to light. In truth, C. declivis from Kiritimati comes in a wide range of colors, with some having mostly yellow or mostly black backs, and with a wide degree of variance in the scale spotting along the sides.

Aquarium care is remarkably simple. Frozen meaty foods are relished, though prepared foods are also well-received. Unless purchased as a bonded pair, only a single individual is recommended. Caution is called for if attempting to mix this fish with others in the butterflyfish family, though this can still usually be accomplished in appropriately sized tanks, and the same advice applies to most acanthurids and larger pomacanthids.