Analysis of proton microprobe data revealed cycles in strontium and calcium in the principal growth axis of the sagitta of the orange roughy Hoplostethus atlanticus (Trachichthyidae: Teleostei). Periodicities in the strontium and calcium composition of orange roughy otoliths
were not related in a constant way to underlying periodicities in the patterns of checks in the otolith. The periodicities in microincrement widths were similar to periodicities of strontium variation in the otolith. The theory of both the physical chemistry of elemental deposition in the
otolith, and the physiology of elemental concentrations in the endolymphatic sac support an extrinsic, annual cycle in otolith strontium content. An extrinsic, annual cycle in otolith strontium content provides a useful tool for evaluation of fish ages estimated from structural and chemical
variation in otoliths.
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