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 Text and photos copyright John P. Hoover

past fishes of the month

FISH OF THE MONTH - MAY 2004

BICOLOR or HAWAIIAN CHUB
Kyphosus hawaiiensis

BICOLOR or HAWAIIAN CHUB
Kyphosus hawaiiensis Sakai & Nakabo, 2004
     Now here's something new--a fish that so greatly resembles the common Gray Chub that ichthyologists never suspected it to be a separate species. Recently, however, two Japanese researchers, Keiichi Sakai and Tetsuji Nakobo, announced that the species which up to now has been called Kyphosus bigibbus is in fact a complex of species. (Ichthyol. Res. 2004, 51: 20-32) They arrived at this conclusion by performing detailed examinations of museum specimens.from all over the world. Specimens from Hawaii, thought to be "Kyphosus bigibbus," were in fact separable into two species that manifested very subtle but consistent anatomical differences. It turns out that neither was bigibbus and both were undescribed. Sakai and Nakobo called one "hawaiiensis" because it occurs only in the Hawaiian and Line Islands, and the other "pacificus" because it is widespread in the Pacific.
      The more common of the two is pacificus. This is the one shown in all the books under the name Gray Chub. (I've included a photo at the bottom of this page.) The other is this month's Fish of the Month. To tell the difference between the two, ichthyologists must perform tedious counts of scales and gill rakers on lab specimens. Luckily, divers and snorkelers can usually tell one from the other fairly easily by color pattern. Like the Gray Chub, the Hawaiian Chub is basically bluish gray, but it typically darkens the posterior half of its body to varying degrees, creating a distinctive half-light half-dark pattern. The habits of the two also differ. The Hawaiian Chub lives in small groups in the surge zone at the top of reefs and dropoffs and can be found reliably in the same locations over a period of years, thus is probably territorial. The Gray Chub, by contrast, often swims in large schools and appears to be much more mobile. Though certainly not rare, the Hawaiian Chub is patchily distributed and rather particular about where it lives. It sometimes aggregates with the Highfin Chub (K. cinerascens), with which it may share habitat. On calm days, snorkelers at Hanauma Bay, O`ahu, can see Hawaiian Chubs at several usually-turbulent spots right on top of the fringing reef in only a few feet of water. The species attains about 14 in. and is restricted to the Hawaiian and Line Islands.

The photo above shows another color pattern which I believe belongs to the Hawaiian Chub, though I don't know for sure. Maybe it's the as-yet-undescribed 5th species that Sakai and Nakobo are working on.

CHUB REVOLUTION!
The species we call Gray Chub in Hawaii (illustrated below and formerly called Kyphosus bigibbus) was given the scientific name Kyphosus pacificus by Sakai and Nakobo. However, Dr. John E. Randall has determined that there is a Hawaiian specimen of this species in the French national museum that in 1880 was named K. sandwicensis. That means that the older name prevails, at least in Hawai`i.(The old biggibus, for those of you who are wondering, is still a valid species, now officially known as the Brown Chub. The Brown Chub occurs in subtropical locations of the Indo-Pacific such as the Red Sea, South Africa, Australia, Japan and Easter Island, but not Hawai`i.) If you are now thoroughly confused by these fishes that look so much alike, here is a list of chubs of the genus Kyphosus known so far from Hawaii. Photos below.

Kyphosus sandwicensis- Gray Chub
ID: often lightish stripe along curve of back; yellow or white color variants
(This is the fish Sakai and Nakobo called pacificus in their paper and that is listed as bigibbus in current Hawai`i fish books)

Kyphosus hawaiiensis - Bicolor or Hawaiian Chub
ID: half & half color pattern pattern, or dark with light central bar.
(This is the new species)

Kyphosus vaigiensis - Lowfin Chub or Brassy Chub
ID: more prominent stripes, often some brassy yellow around mouth and gill cover; becomes dappled or spotted when aroused. (This name is unchanged)

Kyphosus cinerascens - Highfin Chub or Snubnose Chub
ID: snub nose and high soft dorsal fin; silvery to dark with some scales darker than others, producing unkempt, patchy appearance. (This name is unchanged)

          See also Sectator ocyurus - Rainbow Chub

In addition to these, Sakai and Nakobo say that there is yet another chub in Hawai`i which they are in the process of describing. Stay tuned....    

Kyphosus sandwicensis - Gray Chub - yellow variant

Kyphosus cinerascens - Highfin or Snubnose Chub