Relationship between Sr:Ca Ratios in Otoliths of Grey Mullet Mugil cephalus and Ambient Salinity: Validation, Mechanisms, and Applications

Sr:Ca ratios in otoliths of grey mullet Mugil cephalus and ambient salinity: validation, mechanisms, and applications. Zoological Studies 43(1): 74-85. To understand the salinity effect on otolith Sr:Ca ratios, Sr and Ca contents of otoliths of juvenile grey mullet Mugil cephalus reared for 30 d in 8 salinities (0 -35 ) were examined. New increments deposited during the rearing period were discriminated by immersing the acclimated mullet in a tetracycline bath (600 µg/ml) for 24 h to create a fluorescent marker in the otoliths. Ca and Sr contents in the rearing water, fish body, and muscle tissues were measured with an atomic absorption spectrophotometer, and those in the otoliths were measured with an electron probe microanalyzer. Both Ca and Sr contents in the rearing water linearly increased with salinities of from 0 to 35 . The increase in Sr:Ca ratios was non-linear; they increased approximately 2-fold from (7.91 ± 0.41) x 10-3 in 0 freshwater to (15.07 ± 0.63) x 10-3 in 5 seawater and remained constant at (13.95 ± 0.79) x 10-3 in salinities of from 5 to 35 . On the other hand, Ca contents in the new otolith increments deposited in the 30-d rearing period did not change with salinities of 0 -35 , averaging 38.56% ± 0.43%. Sr contents and Sr:Ca ratios in the otoliths increased approximately 2-fold from 0.12% ± 0.01% (Sr) and (3.16 ± 0.36) x 10-3 (Sr:Ca) in 0 freshwater to 0.24% ± 0.03% (Sr) and (6.35 ± 0.70) x 10-3 (Sr:Ca) in 5 -35 seawater, which was consistent with changes in Sr:Ca ratios of the rearing water. In addition, Sr:Ca ratios in the otoliths of fish reared in 5 -35 seawater were negatively correlated with the otolith growth rate. These results indicate that Sr:Ca ratios in otoliths can be used to reconstruct an environmental history of the mullet by differentiating when the fish migrated between fresh water and seawater; however Sr:Ca ratios in the otoliths were affected by salinity and the fish growth rate in an interactive manner. http://www.sinica.edu.tw/zool/zoolstud/43.1/74.pdf