Otoliths as individual indicators: a reappraisal of the link between fish physiology and otolith characteristics

Otoliths are remarkable recorders that store visual and chemical information that can be interpreted with regard to individual fish phenotype trajectory, life history events and environment. However, the information stored in the otoliths must be interpreted with the knowledge that the otolith is an integral part of fish sensory systems. This means that the environmental signals recorded in the otoliths will be regulated by the homeostatic apparatus of the individual fish - its physiology and ultimately its genetic make-up. Although this may complicate interpretation of environmental signals, it also opens up avenues for new research into the physiology and life history of individual fish. This review focuses on research areas where the coupling between otolith characteristics and fish physiology may yield new insights. Most of the research ideas are by no means new, but rather represent largely forgotten or less-explored research areas. Examples of questions that are fundamental, unanswered and with the potential to yield significant new insights are those related to the coupling of otolith and fish growth through metabolism, and the formation of opaque and translucent growth zones in relation to the physiology of the individual. An integration of visual and chemical data with bioenergetic modelling may yield some of the answers.