Selenium incorporation in fish otoliths: effects of selenium and mercury from the water

To study fish migration using otolith microchemistry, it is important to understand the relationship between elements in the otoliths and in the surrounding water, including potential interactions with other elements. Selenium (Se) is a trace element with strong affinity for mercury (Hg). To test if Se is a reliable tracer for fish migration, the effects of dissolved Se and Hg concentrations on Se incorporation in fish otoliths were investigated experimentally. Brown bullheads (Ameiurus nebulosus) were reared in waters spiked with various concentrations of inorganic Se and Hg. Otolith Se:Ca increased nonlinearly with dissolved Se concentrations as there was no significant difference between fish reared in low and medium [Se] waters (Se:Ca for low [Se] waters, 7.64 x 10(-6); medium, 6.59 x 10(-6); high, 1.24 x 10(-5)). Our study also provided the first evidence of a negative effect of Hg on Se incorporation into otoliths (p = 0.01), a phenomenon most evident in high [Se] waters. Because of the influence of Hg, caution should be taken when inferring fish migration based on Se.