Salinities, not diets, affect strontium/calcium ratios in otoliths of Anguilla japonica

Although otolith Strontium (Sr)/calcium (Ca) ratios have been widely used to reconstruct the past salinity environmental history of anguillid eels, factors affecting the Sr/Ca ratios in otoliths are incompletely understood. Japanese Eel (Anguilla japonica) elvers (mean length 54.7±2.1 mm) were collected in the estuary during their upstream migration and reared at 5 different salinities (0, 5, 15, 25, and 35 psu) and 3 types of feeding conditions (formulated feed, tubifex, and starvation) for 30 days to evaluate the effects of salinity and diets on otolith Sr/Ca ratios. Ca and Sr concentrations in the ambient water significantly increased with salinity (SAL) as [Ca] water =15.50SAL−5.56, and [Sr] water =0.21SAL+0.03, respectively. Sr/Ca ratios in otoliths increased with salinity (SAL) of the rearing water as [(Sr/Ca)×1000] otolith=0.091SAL+3.790. In diets, Sr/Ca ratios were 4 times higher in tubifex than in formulated feed. However, in otoliths, ANOVA indicated that Sr/Ca ratios did not differ significantly between groups fed on tubifex or formulated feed (p=0.118). Otolith Sr/Ca ratios were negatively correlated with fish growth rates while the growth rates differed significantly among rearing conditions with different salinities and diets. Partition coefficients of the Sr/Ca ratios from ambient water to fish tissues and otoliths significantly increased with salinity. The Sr/Ca ratios of Japanese Eel otoliths thus were positively correlated with the ambient salinity and decreased with increasing fish growth rate, but was not affected by fish diet. © 2006 Elsevier B.V. All rights reserved.