One Big Butterflyfish!

by B. N. Sullivan

Lined Butterflyfish (Chaetodon lineolatus)

This is the Lined Butterflyfish (Chaetodon lineolatus), perhaps the largest butterflyfish species in the world.  Adults measure about 30 cm (12 in) in length -- nearly twice the size of the majority of butterflyfish species.  The Saddle Butterflyfish (C. ephippium) is the only other butterflyfish species that approaches (and may sometimes match) the size of C. lineolatus.

This is an Indo-Pacific species widely distributed throughout the region.  We have seen them in the Red Sea and in Hawaii, but they are known to occur as well along the shores of East Africa, Southern Japan, and Australia's Great Barrier Reef.

We have observed them almost always in pairs.  They hang out around coral reefs, which is not surprising since they feed primarily on coral polyps.  It is not unusual to see a pair of these fishies bobbing along side by side as they peck away at a coral head.  According to the World Register of Marine Species (WoRMS) page on C. lineolatus, they also feed on anemones, small invertebrates, and algae.

Lined Butterflyfish are believed to be a long-lived species.  Although no one knows for sure how long their natural lifespan is, it is likely several decades.  In places like Hawaii where local divers may visit the same site again and again over years or even decades, the divers learn to recognize individual animals that live there.  We got to know a certain pair of C. lineolatus living in Honaunau Bay, on the South Kona coast of Hawaii Island and have seen them there again and again over a period of at least 15 years.

Honaunau Bay is a popular snorkeling and shore-diving  spot for tourists as well as locals, and many have fed the reef fish there over the years.  While guides and tour operators currently do a good job of discouraging this practice, the fish seem to have long memories.  The pair of Lined Butterflyfish in the image below still approach divers, ever hopeful for a hand-out.

A diver interacts with some Lined Butterflyfish in Honaunau Bay, Hawaii