Identifying sagittal otoliths of Mediterranean Sea gobies: variability among phylogenetic lineages

Abstract

In this study, we describe and analyse the morphology of the sagitta, the largest otolith, of 25 species of Gobiidae inhabiting the Adriatic and north-western Mediterranean seas. Our goal was to test the usefulness and efficiency of sagittal otoliths for species identification. Our analysis of otolith contours was based on mathematical descriptors called wavelets, which are related to multi-scale decompositions of contours. Two methods of classification were used: an iterative system based on 10 wavelets that searches the Anàlisi de Formes d'Otòlits (AFORO) database and a discriminant method based only on the fifth wavelet. With the exception of paedomorphic species, the results showed that otolith anatomy and morphometry can be used as diagnostic characters distinguishing the three Mediterranean phylogenetic goby lineages (Pomatoschistus or sand-goby lineage, Aphia lineage and Gobius lineage). The main anatomical differences were related to overall shape (square to rhomboid), the development and shape of the postero-dorsal and antero-ventral lobes and the degree of convexity of dorsal and ventral margins. Iterative classifications and discriminant analysis of otolith contour provided very similar results. In both cases, more than 70% of specimens were correctly classified to species and more than 80% to genus. Iterations in the larger AFORO database (including 216 families of teleosts) attained a 100% correct classification at the family level.

Identification of fish families and species from the western Arabian Gulf by otolith shape analysis and factors affecting the identification process

“…We proposed two multivariate statistical approaches for the case of incomplete species list. If the number of species included in the analysis is limited, plotting all samples over a plot after some dimension-reduction method, such as canonical analysis of principal coordinates (Libungan and Pálsson 2015) and canonical variate analysis (Lombarte et al 2018), could be used as a preliminary tool to detect outlier specimens. If the sample size of fishes and number of species is sufficiently large, then it could be reasonable to assume that within-and between-species variability is well represented.…”

“…The otoliths of some fish species become greatly curved towards the external face and their three-dimensional (3D) structures become more apparent as the fish grows. Thus, it was not feasible to obtain otolith photographs in which all the otoliths were positioned in a perfect horizontal plane with the sulcus acusticus facing the observer, as done by Lombarte et al (2018). Alternatively, the otoliths were placed horizontally with the external plane of the otolith facing towards the observer (Fig.…”

“…Although otolith shape analysis is a promising tool for the identification of fish groups, several factors may hinder its successful use, the first being the selection of available analytical methods. Differences in otolith shape have been used to identify teleost species for over 130 years (Nolf 2013;Lombarte et al 2018) and numerous analytical approaches have been developed (e.g. Tuset et al 2003Tuset et al , 2016Ponton 2006;Wakefield et al 2014;Libungan and Pálsson 2015).…”

“…Second, identification performance may be affected by the number of candidate species. Lombarte et al (2018) suggested an inverse relationship between the correct identification rate and the number of candidate species based on a summary of six studies. However, these studies differed in methodology and collection sites, and the relationship has not been tested in a systematic manner using the same methodology in a single study.…”

Otolith measurements to estimate standard length of gobiid fish (Teleostei: Gobiiformes) from the Persian Gulf and Oman Sea

“…Otolith is calcareous structure located in the inner ear of teleostean fish (Popper et al, 2005). Among three types of otoliths, sagittae have diverse morphology in most groups of fish and employed in taxonomy (Lombarte et al, 2018), paleontology (Reichenbacher et al, 2018) and fisheries management (Carlson et al, 2017).…”