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17-20 Johnston Atoll
17-20, The endemic angelfish of Johnston Atoll
of June 8, 2006
Dr. Malia Rivera
The spectacular rainbow pygmy angelfish endemic to Johnston Atoll. Photo by L. Rocha.
Jenny Schultz, a Ph.D. student in the lab of Dr. Brian Bowen of the Hawai‘i Institute of
Marine Biology, is trying to work out the evolutionary relationships between a group of
angelfishes from a genus called Centropyge. Commonly known as the pygmy angelfishes,
worldwide there are about 32 species, just a handful in the Atlantic, the majority
occurring in the Pacific. Spectacular colors and shapes of these little fishes have
made them extremely popular in the aquarium trade.
Like most researchers in Brian’s lab, Jenny is using sophisticated DNA analyses to delve into questions as to just how and where the angelfishes of the world have speciated (i.e., formed new species), and whether the presently described morphological (shape) and color differences between species are consistent with their genetic differences. She is particularly excited about a few new samples she obtained with the help of Dr. Randy Kosaki, Research Coordinator for the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve. It just so happens that about 15 years ago, Randy discovered Johnston Atoll’s only endemic species, the pygmy angelfish he named Centropyge
nahackyi, also called the rainbow pygmy angelfish. Another species, the Potter’s pygmy, is endemic to both the Hawai‘i and Johnston.
The Potter's pygmy angelfish is endemic to both Hawai'i and Johnston Atoll.
Photo by M. Rivera.
The beautiful rainbow pygmy is one of just a few species Jenny hasn’t yet analyzed with genetics.
From her laboratory work so far, she has been finding some very interesting patterns in the DNA
comparisons. “There are a few species that are accepted as distinct species based on their color
differences, but it appears they have no distinguishable genetic differences with the DNA markers
I have examined.” What this might imply is that either these supposedly different angelfishes
are not “true” species and may need further study to clarify their status, or they have so recently
separated into new species that their genetic signatures still remain very similar even if they
no longer interbreed with each other. For the rainbow pygmy, it is most likely that its closest
relative is the multicolored pygmy from the Western Pacific, this based on similarities in
shape and color patterns. Both Randy and Jenny are eager to see the outcome of the DNA work
to see if this hypothesis holds true.
Why does any of this matter to managers? Most conservation biologists agree that it is
difficult to effectively manage ecosystems, and the species they contain, if you don’t
even know what kinds and how many species exist in the system. Perhaps many species are
out there that biologists aren’t even aware of because they look so similar to other
species, a situation they call “cryptic” species. Conversely, many so-called different
species might in fact be the same, and just harbor a lot of color variation among individuals.
Randy Kosaki captures live specimens of the rainbow pygmy for
Aquarium. Photo by J. Zamzow.
With the support from the U.S. Fish and Wildlife Service, the government agency responsible
for Johnston Atoll’s wildlife management, Randy has captured a handful of the rainbow pygmy
for delivery to the University of Hawaii’s Waikiki Aquarium. At this moment they are
contained in a large cooler filled with sea water, and will be promptly delivered to the
Aquarium for display upon the return of Hi‘ialakai to Honolulu. These beautiful fish are
certainly worth a visit to see first hand just how the Hawai‘i Institute of Marine Biology,
the U.S. Fish and Wildlife Service, and the NWHI Coral Reef Ecosystem Reserve are working
together to protect our precious coral reef resources.