Peeling the Otolith of Fish: Optimal Parameterization for Micro-CT Scanning

Abstract

In this paper, we aim to provide optimal parameters for micro-computed tomography scans of fish otoliths. We tested fifteen different combinations to sagittae. The images were scaled to Hounsfield units, and segmented in two distinct volumes-of-interest (external and internal). The strategy we applied, for identifying optimum scan settings for otoliths, included analyses of the sinogram, the distribution of the Hounsfield units and the signal-to-noise ratio. Based on these tests, the optimum sets of parameters for the acquisition of tomographic images of sagittal otoilths were 80 kV, 220 µA, and 0.5 mm aluminum filter. The method allowed 3D shape analysis, internal and external density distribution, layer-by-layer density segmentation, and a potential objective method to count growth rings in otoliths. It was possible to compare mean densities between species, and we observed a significant difference among them. In addition, there are ontogenic changes, which could be increasing or decreasing the density. In this study, we applied tomography for several otolith analysis, that could be of great interest for future studies in diverse areas that use otoliths as the basic structure of analysis, or represents a new research line called eco-densitometry of otoliths, where tomography could be applied to explore the density within an ecological perspective.

Microtomographic investigation of a large corpus of cichlids

“…To the best of our knowledge, no fully automated method for non-destructive otolith extraction from high-resolution tomographic data has been published up to now.. Vasconcelos-Filho et al [ 37 ] show a potentially objective method to count growth rings in otoliths of six fish species, but performed their study on extracted otoliths “embedded in a Styrofoam cube”, while our method non-destructively extracts the otoliths from the tomographic data. Gu et al [ 38 ].…”

Radiological characterization of gilthead seabream (Sparus aurata) by X‐ray computed tomography

“…These structures are used in studies regarding age, migration, population structure, phylogeny, feeding behaviour of fish with carnivorous preferences (as in the case of gilthead seabream) and life histories, constituting an important tool in diverse fields of ichthyology and fishery science (Duarte‐Neto et al ., 2008; Granadeiro & Silva, 2000; Green et al ., 2009; Panfili et al ., 2002). Currently, CT is one of the emerging techniques with perhaps the greatest potential for the study of fish otoliths (Vasconcelos‐Filho et al ., 2019). Its application has been demonstrated in previous studies where a correlation between CT values and different water pollution degrees was achieved (Yan et al ., 2009).…”

Magnetic actuation of otoliths allows behavioral and brain-wide neuronal exploration of vestibulo-motor processing in larval zebrafish

“…with ρ p = 4.8 g cm −3 the density of the ferrofuid particles (maghemite, γ − F e 2 O 3 ) (www.matweb.com), and ρ ot = 2.93 g cm −3 the density of the otolith 33 .…”