CYCLOTHONE KOBAYASHII, A NEW GONOSTOMATID FISH (TELEOSTEI, STOMIIFORMES) FROM THE SOUTHERN-OCEAN, WITH NOTES ON ITS ECOLOGY

A new gonostomatid fish, Cyclothone kobayashii, is described on the ba sis of specimens taken from the Southern Ocean and adjacent waters sou th of 30 degrees S. Among the other 12 currently recognized species, C . Kobayashii is most similar to C. pseudopallida but is readily distin guished from it by the absence of the following internal sagittal pigm entation (except for a few punctate melanophores): patches of pigment between successive neural spines anterior to dorsal-fin origin; puncta te/dispersed melanophores along spinal cord; and streaks of pigment al ong neural and hemal spines. The higher VC photophore counts [(20)21-2 2 vs 18-20] also are useful in distinguishing these two species, where as other meristic characters overlap each other to varying degrees. Cy clothone kobayashii is abundant in the Southern Ocean around 35-45 deg rees S, its range extending southward to 60-65 degrees S and northward to 25-35 degrees S (rarely to 10 degrees S). It is replaced by C. pse udopallida in the more northern latitudes, and the two species occasio nally occur together between 25 degrees S and 35 degrees 5. Although t here are no data on the actual depths of occurrence for C. kobayashii, circumstantial evidence suggests that it occupies the midlayer betwee n the shallower C. braueri and the deeper C. microdon. Cyclothone koba gashii occurs deeper than C. pseudopallida when sympatric. Examination of gonads from selected specimens demonstrated that reproductive char acteristics of C. kobayashii are very similar to those of C. pseudopal lida. On the basis of the supposed sister-group relationship between C . kobayashii and C. pseudopallida, it seems reasonable to postulate th at their separate, though slightly overlapping distributions, have bee n achieved through some large scale oceanographic subdivision of their common, circumglobal ancestral population. A revised key is provided for Cyclothone of the Southern Ocean and adjacent waters south of 30 d egrees S.