Otolith Biochemistry—A Review

Abstract

Otoliths are bioinorganic minerals within the inner ear of all bony fishes. They grow incrementally, laying down alternating protein-rich and mineral-rich bands daily. Consequently, otoliths are considered natural chronometers, archiving the growth and physico-chemical histories of individual fish, and thus are a powerful resource for fish biologists and fisheries managers. To date, otolith research has focused primarily on the measurement of otolith increments for age and growth studies and to a lesser extent on the analysis of trace-element:calcium ratios for reconstructing past environments. In contrast, little attention has been paid to the proteinaceous constituents of the otolith, their mechanisms of incorporation or their implications for otolith formation, growth and chemical composition. To provide a picture of the current state-of-knowledge, 228 papers relating to otolith biochemistry were reviewed, producing a comprehensive summary of the biochemistry of the endolymph, saccular epithelial tissues, and the otolith. Furthermore, this review presents a discussion of the structure and function of the 28 proteins and 5 proteoglycans identified thus far, provides comments on the appropriateness and utility of trace elements as environmental proxies, and suggests fruitful lines of future research in otolith science.

Keywords:

• Otolith
• biomineralization
• proteomics
• inner ear
• endolymph

Acknowledgements

The authors thank S. Mukherjee and S. Klatt for their invaluable advice and comments.

Additional information

Funding

This work was supported by the Australian Research Council under Grant LP140100087. ORBT was supported by an Australian Postgraduate Award.