Otoliths have served as natural recorders of fish life-history information for over a century. Many of the analytical methodologies developed for otoliths have been further applied to other calcified structures in aquatic organisms and those techniques have provided analogous biological, ecological and environmental information. This special issue includes a selection of papers that were presented in the 6th International Otolith Symposium in Taiwan and highlight the recent developments and advances of otolith research.

Fish ear stones, or otoliths, contain a remarkable amount of information encoded in their chemical compositions. Metaphorically, otolith chemical patterns reflect the lives of fishes much like a painting reflects the point of view of an artist. This review uses this artistic metaphor to explore recent advances in the use of otolith chemistry as a technique to assess ecological dynamics of fishes.

Otolith increments and chemistry have undeniably advanced the understanding of fish biology. We applied these tools to investigate the early life history of an important finfish that recruited to a single nursery, and identified significant variation in age, growth, hatch date and elemental chemistry within and between years. Our results highlight the importance of considering temporal variation in otolith studies.

Understanding fish movements from nursery areas to reefs is important for marine conservation, but the availability of such information is limited in Malaysia. To retrospectively track habitat uses of Lethrinus lentjan, otolith and muscle tissues of adults and juveniles were used. The results showed the connection between inshore and offshore habitats, but coastal currents driven by monsoons may affect the direction of fish migration.

Clear Lake hitch is an imperilled minnow that migrates from the sole lake it occupies into ephemeral tributary streams for spawning. Natural tags (isotope ratios of strontium) recorded in otoliths can identify the birth stream and age when the Clear Lake Hitch emigrated to the lake. With this new tool it is now possible to reconstruct habitats and life history strategies contributing to the successful production and recruitment of Clear Lake hitch.

This study evaluated the efficiency of marking statoliths of Sepioteuthis lessoniana embryos with enriched ¹³⁷Ba and highlighted the potential effects on the size-at-hatch and statolith chemistry of individuals after marking for future application in the field.

The delineation of appropriate management units is essential for an effective management of a species. Ear-bone chemical composition proved to have the potential to identify the mixing range and structuring of a commercially important tropical tuna species, the yellowfin tuna. This information will help develop a sustainable harvesting strategy in a fishery with an ever-increasing global demand.

We show how the suitability of using the chemical composition of shark vertebrae as a natural tag is element specific and likely governed by a suite of potentially codependent environmental and physiological factors. By unravelling how these factors contribute to element chemistry, we further advance the use of vertebrae chemistry as a tracer of shark movements.

This study estimated the movement patterns of Pangasius krempfi, a vulnerable catfish in the Mekong River. The study confirmed that this species is anadromous and migrates from fresh water to water with higher salinities to grow. P. krempfi may return to hatching habitats when older, and will then be threatened if the connectivity between habitats is stopped in the future by the construction of dams along the river.

Carbon isotope values recorded in fish otoliths provide a possibility to investigate field metabolic rate. The otolith δ¹³C metabolic proxy in combination with other newly valuable and well-established approaches allows us to track the effects of ontogenetic and environmental drivers on individual fish physiology, and removes a major obstacle to understanding and predicting the performance of free-ranging wild fish.

Nitrogen and carbon isotope analyses can provide information about the trophic positions of fish. Otoliths and muscle and heart tissue from cod raised at four different temperatures were analysed to evaluate whether the isotopic signal was biased by the temperatures experienced. The results indicate that the trophic signals recorded will reflect the diet of the fish across temperatures.

A radiocarbon signal produced by testing nuclear bombs in the atmosphere has been used to age fishes for 25 years, but the method was limited to birth years later than 1958. Although validated to a minimum age near 40 years, the longevity of red snapper (Lutjanus campechanus) was unresolved until its otoliths were analysed for radiocarbon using laser ablation–accelerator mass spectrometry, with confirmation of a 60-year lifespan.

Fish growth in the cold lakes of the Arctic would be expected to be very low, but previous studies have suggested otherwise. Radioactive remnants from nuclear weapons tests in the 1950s were used as dated markers to confirm very low growth and mortality rates, and longevities exceeding 50 years, in an unfished lake whitefish (Coregonus clupeaformis) population in the Arctic.

Daily and yearly ages of striped marlin were estimated by counts of otolith microincrements and dorsal fin spine annuli using specimens caught in the tropical eastern North Pacific. The species in the area grow, on average, to over 100 cm within 4 months. Age composition was different among three subregions in the eastern North Pacific.

The phenotypical variability in otolith shape of anchoveta (Engraulis ringens) among three zones (I, II and III) from north to south along the Chilean coast supports the hypothesis that juveniles and adults of anchoveta have remained segregated throughout their entire, or at least a fraction of, their life cycle, mainly between the extreme northward (Zone I) and southward (Zone III) zones.

We investigated the appearance and ecological role of a new male morph of the squid Doryteuthis gahi using several datasets. The results suggest that superbulls from the autumn spawning cohort are older than the residual population, and are likely providing connectivity between the two spawning cohorts. There is a significant environmental effect on size at age, suggesting superbulls arise through phenotypic plasticity.

Otolith shape analysis was used to identify 16 fish species belong to 5 families from the western Arabian Gulf and factors potentially affecting the performance of this process were investigated. Having multiple data sources, information a priori to reduce the number of candidate species and sufficiently large sample sizes across wide size ranges are key to the precise identification of families and species.

Taking measurement error into account in a biological model may be of particular interest depending on the context in which the measurements are to be used. Repeatability in growth and age estimation at the individual level has a significant effect on estimating parameters at the population level. In this study we determined to what extent interscale (intraindividual) and inter-reader effects were negligible compared with interindividual variability, providing a rationale for selecting an appropriate sampling strategy.

We developed a Monte Carlo simulation model to evaluate the effects of fish otolith sampling methods and ageing error (bias and imprecision) on estimations of age composition and growth curves of the Pacific bluefin tuna (Thunnus orientalis). The findings from this study can be used to provide guidelines for fish otolith sampling strategies and minimum otolith sample sizes.