Hicks, B. J., West, D. W., Barry, B. J., Markwitz, A., Baker, C. F. & Mitchell, C. P. (2005). Chronosequences of strontium in the otoliths of two New Zealand migratory freshwater fish, inanga (Galaxias maculatus) and koaro (G. brevipinnis). International Journal of Particle Induced X-ray Emission 15(3-4), 95-101.
Permanent Research Commons link: http://hdl.handle.net/10289/2211
Half of the freshwater fish fauna in New Zealand is diadromous (i.e., migrates between the sea and freshwater); unimpeded access to and from the sea is important for the conservation of diadromous fish. The genus Galaxias (Galaxiidae: Osmeriformes) contains five diadromous species that spawn in freshwater, migrate to sea as larvae, and then migrate back into freshwater as 50-55-mm juveniles. Microchemistry of the otolith, a calcified structure in the fish's head, allows an independent test of assumptions about these migrations. Concentric layers of CaCO3 with some Sr as SrCO3 comprise the otolith, creating a chronosequence that reflects a fish's migratory history. More Sr accumulates in the otolith when a fish is in seawater than when it is in freshwater. High-resolution nuclear microscopy was used to measure the molar ratios of Sr/Ca in two galaxiid species. Otoliths of inanga (G. maculatus) caught in freshwater all showed a central zone of 100-200 μm in radius with Sr/Ca of 0.008-0.012, indicating early rearing in the sea. Sr/Ca values decreased to 0.001-0.002 as the fish moved into freshwater. Of six adult koaro (G. brevipinnis) caught in a river with sea access and no lakes, five had migrated to sea but one had not, raising questions about the generalized assumptions of migration.
World Scientific Publishing Co. Pte. Ltd.
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