Trace Metal Deposition in Teleost Fish Otolith as an Environmental Indicator

Arai, Takaomi; Ohji, Madoka; Hirata, Takafumi

Trace Metal Deposition in Teleost Fish Otolith as an Environmental Indicator

2007

Arai, Takaomi | Ohji, Madoka | Hirata, Takafumi

Trace metal levels in the otoliths of the juvenile chum salmon Oncorhynchus keta were examined by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Life history transect analyses showed that all otoliths had a central region with low Zn/Ca ratios (mean, 0.35-0.68 x 10-⁴), and thereafter the ratios increased abruptly in the freshwater growth zone (mean: 1.72-1.90 x 10-⁴) toward the edge of otolith. In regard to otolith Sr/Ca ratios, all specimens showed slightly higher values in the otolith core region, and thereafter the ratios showed constant values or values that decreased gradually toward the edge of the otolith in the freshwater growth zone (mean, 3.33-4.58 x 10-³). An abrupt increase was found in some specimens to 5-7 x 10-³ in the maximum levels around the otolith edge. The relationship between Sr/Ca and Zn/Ca ratios at each ablation in otoliths in both juvenile and adult salmons showed a significant correlation. Otolith Zn/Ca and Sr/Ca ratio patterns were seen to reflect the levels in ambient water environment. Thus, these findings indicate that Zn, like Sr, in teleost otoliths is an excellent tracer for reconstructing the ambient aquatic environmental conditions which individual fish have experienced.

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