Application of UV-cured resin as embedding/mounting media for practical, time-saving otolith specimen preparation

Abstract

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