Hawaii's Milletseed Butterflyfish (Chaetodon miliaris)

by B. N. Sullivan

Here's another Butterflyfish from Hawaii. This one is called the Milletseed Butterflyfish (Chaetodon miliaris), although you also may see it identified in some picture books as the Lemon Butterflyfish. Which common name you prefer may depend on whether you focus on its lemony background color, or its vertical rows of black spots.  The scientist who named the species focused on the spots, which he thought resembled milletseeds, hence  the species name miliaris.

Like the Multiband Butterflyfish (Chaetodon multicinctus that we presented in the previous post, C. miliaris is a Hawaiian endemic species.  In fact, the two species are closely related, both belonging to the subgenus Exornator. Nevertheless, the behavior of the two species is different in several ways.

Most conspicuously, the Milletseed Butterflyfish lives in aggregations instead of in pairs, and they are not territorial. It is not uncommon to see whole mobs of these bright yellow fishies moving along the reef together, looking for food.  Now,  "mob" is hardly a scientific term, but it suits shoals of Milletseed Butterflyfish.  Unlike some other fishes that school and move along in an orderly way, almost in unison, the Milletseeds move along together in an almost rowdy fashion -- but  I must say, that is a wonderful sight to behold.

Milletseed Butterflyfish have a much more varied diet than C. multicinctus. Their preferred food is zooplankton, but they also will eat the eggs of other fishes -- especially those of fishes that deposit egg masses on rocks and other surfaces.  Milletseeds sometimes perform as cleaners of other fishes, too.

The Milletseed Butterflyfish occurs naturally only in Hawaii, but it is not rare in the islands.  In fact, C. miliaris is said to be the most common among the 24 species of the Butterflyfish family (Chaetodontidae)  found in the Hawaiian islands.  If you dive or snorkel in coral reef environments in Hawaii you are almost certain to encounter a 'mob' of these yellow beauties.