Redtail butterflyfish

Lore & Background

The red-tailed butterflyfish is brown to black, with lighter scales giving it a spotted appearance. It has a prominent vertical white streak behind the eyes, a dark stripe over the eyes, and a smaller white stripe in front of the eyes. The base of the tail is bright red, followed by a black stripe, and the tip of the tail is diffuse white. It belongs to the large subgenus Rabdophorus, which might warrant recognition as a distinct genus. Its relationships within this group are doubtful; it seems related to the 'raccoon-masked' group including the black butterflyfish (C. flavirostris), diagonal butterflyfish (C. fasciatus), Philippine butterflyfish (C. adiergastos), and the raccoon butterflyfish (C. lunula), though its color and pattern are entirely different from these, sharing only the robust habitus and bold habits.

Reader's Guide

The red-tailed butterflyfish is significant in the study of butterflyfish evolution due to its near-match in appearance with the mailed butterflyfish (C. reticulatus), despite DNA sequence and osteology data overwhelmingly placing C. reticulatus in a different subgenus called 'Citharoedus' (a name preoccupied by a mollusc genus). This subgenus contains fish like the scrawled butterflyfish (C. meyeri), which has a 'finger-painted' pattern of uneven lines on a light silvery background. If Rabdophorus were considered a distinct genus, 'Citharoedus' would not be included in it but placed with the subgenera Lepidochaetodon or Megaprotodon. Thus, the red-tailed and mailed butterflyfishes probably represent a case of convergent evolution and perhaps mimicry, though the selection forces responsible for their striking similarity are not known. A highly anomalous 12S rRNA mtDNA sequence found in this species in one 2007 study seems to be due to a laboratory error; another study found a 12S rRNA sequence agreeing with the general pattern of mtDNA evolution in Rabdophorus.

Did You Know?

• It can grow to 18 cm (over 7 in) in length.
• Its diet in the wild consists of coral polyps; in captivity it eats fish meat and shrimp.
• The mailed butterflyfish (C. reticulatus) is a near-match in appearance but has a less brown hue and light blue instead of red in its tail.