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Occurrence of the non-anadromous life history in the shirauo, Salangichthys microdon


Author's address: Takaomi Arai, International Coastal Research Center, Ocean Research Institute, The University of Tokyo, 2-106-1, Akahama, Otsuchi, Iwate 028-1102, Japan.


Strontium (Sr) and calcium (Ca) concentrations in the otoliths of the shirauo, Salangichthys microdon, collected from Japanese coastal waters were examined by wavelength-dispersive X-ray spectrometry on an electron microprobe. The otolith Sr : Ca ratios gradually increased from 15.7−19.7 × 10−3 around the core to 32.8−39.4 × 10−3 around the edge of otoliths, with no transition point from the low Sr : Ca ratio phase to the high phase. The fluctuation pattern of otolith Sr : Ca ratios was different from the anadromous form reported in a previous study. The evidence indicates that the fish do not necessarily migrate into freshwater during the growth phase.