Multiscale analysis on otolith structural features reveals differences in ontogenesis and sex in Merluccius merluccius in the western Adriatic Sea

Abstract

Otolith biomineralization results from biochemical processes regulated by the interaction of internal (physiological) and external (environmental) factors which lead to morphological and ultrastructural variability at intra- and interspecific levels. The aim of this study was to conduct a multi-scale analysis of the sagittal otoliths of the Merlucius merlucius (European hake) from the western Adriatic Sea in order to correlate otolith features with fish ontogeny and sex. We show that otoliths of sexually undifferentiated (non-sexed) individuals having a fish body total length (TL) less than 15 cm had faster growth in length, width, area, perimeter, volume and weight and a higher amount of organic matrix compared with otoliths of sexually differentiated individuals (females and males) having a fish size range of 15–50 cm. Most importantly, with increasing fish TL, female saccular otoliths contained a higher number of protuberances and rougher surface compared with male specimens, which showed more uniform mean curvature density. The differences between females and males discovered in this study could be associated with fish hearing adaptation to reproductive behavioural strategies during the spawning season. The outcomes of this research provide insights on how size and sex-related variations in otolith features may be affected by fish ecological and behavioural patterns.

Heterogeneity of otolith chemical composition from two‐dimensional mapping: Relationship with biomineralization mechanisms and implications for microchemistry analyses

“…Although we treat 2D spatial variation in this study, with a focus toward asymmetric distribution between the proximal and distal sides of the otolith, variability in elemental concentration also occurs in three dimensions. 3D variability of otolith structure is a nascent and promising field of research (e.g., Barry et al, 2008; Palazzo et al, 2022), although variability in 3D otolith chemistry has not yet been treated in the scientific literature, with the implicit assumption, in the absence of further information, that all planes of a sectioned otolith should provide equivalent chemical information. In demonstrating that there is variability in the concentration of elements within a single otolith section, it is logical to suggest that similar variability may occur in three dimensions, for the same reasons as those discussed for a 2D plane.…”