Cook Island color form of N. helfrichi - compare the head coloration with that of the two specimens from Micronesia above.
There are probably a lot of you out there that encountered their first Nemateleotris helfrichi within the pages of Helmut Debelius’ FISHES FOR THE INVERTEBRATE AQUARIUM? I received a copy of this book in the mid-1980’s and was blown away by Helfrich’s dart or firefish! While the fish was new to me, it certainly was not new to science, having been described by Dr. Jack Randall and Dr. Gerald Allen all the way back in 1973.
This lovely fish is known to occur around the Ryuku and Ogasawara Islands, in Micronesia and Polynesia (the type locality being Tahiti). This fish started making its way into aquarium stores (to the best of my recollection) in around 1991 or 1992. The first specimens I was able to buy were from Micronesia. They had the characteristic coloration of the fish pictured in Debelius’ book. This same color form appears in John Randall’s FISHES OF THE SOUTH PACIFIC. He describes the coloration of the fish as follows:
“..lavender, gradually shading posteriorly nearly to white and anteriorly on head to bright yellow; top of head from interorbital to origin of first dorsal fin with a narrowing band of bright magenta, merging with violet on dorso-anterior quadrant of iris; elevated anterior part of first dorsal fin orange and back with a broad, pale blue leading edge; rays of second dorsal and anal fins tipped with yellow or orange caudal fin pale yellow.”
This certainly describes the populations of N. helfrichi from Micronesia and Japan "to a T." But it turns out that the population of N. helfrichi from Polynesia is quite different chromatically. I had seen photos of N. helfrichi from this region before and knew the color differed. But recently my good friend Kevin Kohen was able to acquire some live specimens from the Cook Islands. While very expensive, I wanted to see this “color form” of N. helfrichi first hand and take photos of it.
As you can see from the photos above, the Cook Island fish differs rather dramatically from its Japanese/Micronesian cousin. Note for example the differences in the color of the head, the metallic blue on the “face,” the black line over the upper jaw and the subtle differences in coloration of the anal fin.
The holotype for the species N. helfrichi is a specimen from Tahiti (Randall and Allen 1973). Not surprisingly, the holotype is the same color as the Cook Island fish. That would suggest that the Polynesian fish are actually N. helfrichi, while the Micronesian/Japanese populations MAY represent an undescribed species. DNA analysis will be needed to emphatically answer this question. More to come on this one in the future.
© Scott W. Michael