Directional bilateral asymmetry in otolith morphology may affect fish stock discrimination based on otolith shape analysis

Abstract

Otolith shape analysis is an efficient fish stock identification tool. However, most applications used left and right otoliths or only one of them arbitrarily chosen without testing for biases resulting from potential directional bilateral asymmetry (DA) in otolith shape, i.e. a unimodal population-level deviation form bilateral symmetry between right and left otolith shapes. In this study, 560 bogues (Boops boops) were sampled from 11 geographical locations from the Canary Islands to the Aegean Sea and elliptical Fourier descriptors were used to describe their otoliths’ shape. First, a significant otolith DA was observed at the global scale with an average amplitude of 2.77%. However, at the scale of sampling locations, DA was not always significant and varied in amplitude and direction. Second, population structure was investigated using the shape of either right otoliths or left otoliths or both together. Analyses based on right otoliths or both otoliths together, suggested three stock units: a North-Western Mediterranean Sea stock, an Eastern Mediterranean Sea stock, and a Central-Eastern Atlantic Ocean and South-Western Mediterranean Sea stock. In contrast, no coherent geographical pattern was found based on left otoliths. Our results highlight the importance of accounting for potential otolith DA in otolith shape-based stock identification.

Fish size effect on sagittal otolith outer shape variability in round gobyNeogobius melanostomus(Pallas 1814)

“…No of pair# Asteriscus shape in N. melanostomus, and its otolith size is also associated with sound production (Lugli et al, 1997). Interestingly, DA is observed for one roundfish species in some geographical areas, whereas it is not in others (Mahe et al, 2019). Mille et al (2016) suggest that food quantities influence fish otolith structure, opacity and shape, and diet composition has an effect on otolith chemical composition.…”

“…In the other classes, the similarity measure ranged from 77.9 to 91.8%. Mahe et al (2019) mention that in addition to interindividual variation in roundfishes, otolith shape is known to vary intra-individually because otolith shape is not always bilaterally symmetrical in pairs. Deviations from bilateral symmetry in roundfish otolith shape reportedly result from fluctuating and/or directional asymmetries (FA and DA, respectively; Lychakov, 2013) associated with differences in carbonate accretion rates.…”

Stock discrimination of the bogue, Boops boops (Actinopterygii: Perciformes: Sparidae), from two Tunisian marine stations using the otolith shape

“…In addition, Ferri et al (2018) studied the variability of the otolith morphology and morphometry in six juvenile specimens collected from the eastern coastal Adriatic region and recorded variations in the sagittae shape, margins, and anterior region among the studied juveniles. Moreover, Mahé et al (2019) analyzed the directional bilateral asymmetry of otoliths in specimens collected from 11 geographical regions from the Canary Islands to the Aegean Sea using elliptical Fourier descriptors and found a significant otolith bilateral asymmetry at the global scale and non-significant asymmetry at the scale of sampling locations.…”

Loss of Coilia nasus habitats in Chinese freshwater lakes: An otolith microchemistry assessment

“…Consequently, it will be necessary to develop corresponding methodologies based on the present study, cooperating with more targeted otolith-based approaches. These include otolith shape-based population or ecotype discrimination [ 71 , 72 ], multiple element-based spatiotemporal habitat reconstruction [ 44 , 73 ], and heavy metal-based anthropological environmental impact/pollution monitoring [ 74 , 75 ] that are designed to enable more accurate monitoring of the dynamics of different C. nasus ecotypes, the development of landlocked/freshwater resident population, the vulnerability of anadromous C. nasus to lacustrine pollutants (e.g., heavy metal) or habitat degradation. This will help in the more effective establishment of natural refugia and reserves in the lakes to conserve and enhance the populations of anadromous C. nasus .…”