19Otoliths are calcified structures located in the inner ears of fish, as in most vertebrates, 20 that are responsible primarily for the perception of gravity, balance and movement, and 21 secondarily of sound detection. Microstructural and chemical analyzes of the inner otolith 22 growth layers, called increments, constitute powerful tools to estimate fish age and 23 elucidate many life history and demographic traits of fish populations. Otolith analyzes 24 often require the production of a thin cross section that includes in the same plane of view 25 the otolith core and all microscopic layers formed from birth until the moment of collection 26 (otolith edge). Here we report on the usefulness of UV-cured resins that have become recently 27 popular among nail artists and hobbyists for otolith specimen preparation. We show that 28 single-component UV-cured resins can replace successfully and advantageously the 29 commonly used two-component Epoxy resins to obtain otolith cross sections suitable for 30 both microstructural examination and chemical analysis by electron probe microanalysis. 31 UV-cured resins provide on-demand, extremely rapid (minute-order) hardening and high 32 transparency, while providing similar adhesion and mechanical support for the otoliths 33 during processing and analysis as Epoxy resins. UV-cured resins may revolutionize 34 otolith specimen preparation practically-and time-wise, and may be particularly useful 35 in teaching and workshop situations in which time for otolith embedding is a constraint.36 37

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The amount of interspecific and ontogenetic variation in otolith shape among clupeid fishes from Japan was investigated to create a key to identify otoliths of these species found in the stomach contents of piscivorous predators, fossiliferous beds, and archaeological sites. The interspecific comparison with 12 species (Clupea pallasii, Etrumeus micropus, Herklotsichthys quadrimaculatus, Ilisha elongata, Konosirus punctatus, Nematalosa come, Nematalosa japonica, Sardinella aurita, Sardinella melanura, Sardinella zunasi, Sardinops melanostictus, and Spratelloides gracilis) revealed morphological variation in otolith shape, OL:OH and AL:RL ratios, rostrum, marginal structures, and features of the crista superior. Intraspecific changes were analyzed in two species (E. micropus and S. melanostictus), revealing ontogenetic changes in OL:OH ratio and consequently otolith shape as well as changes in marginal features. Overall, this study shows that the key morphological features can be used as diagnostic features for identification of clupeid otoliths.

No abstract

Otoliths are calcified structures that are located in the inner ears of fish, as in most vertebrates, that are responsible primarily for the perception of gravity, balance, and movement and secondarily of sound detection. Microstructural and chemical analyses of the inner otolith growth layers, called increments, constitute powerful tools for estimating fish age and elucidate many life history and demographic traits of fish populations. Otolith analyses often require the production of a thin cross section that includes the otolith core and all increments formed from birth (core) until the moment of collection (otolith edge) in the same plane of view. Here we report on the suitability of single-component UV-cured resins to obtain otolith cross sections for both microstructural examination and chemical analysis by electron probe microanalysis. Embedding blocks that were produced with UV-cured resins had transparency that was comparable to that of the commonly used two-component epoxy resins and provided similar adhesion and mechanical support for the otoliths during grinding or cutting with a precision cutter and analysis. In addition, UV-cured resins offer on-demand, extremely rapid (minute-order) hardening that makes them useful in classroom situations in which time for otolith embedding becomes a constraint.