Distinct inter and intrapopulation variation in the otolith shape and size of Mullus barbatus (Actinopterygii: Mullidae) from the Bizerte and Ghar El Melh lagoons in Tunisian waters

ABSTRACT

This study aimed to assess the geographic variation in otoliths’ shape and size and the effect of potential fluctuating asymmetry (FA) in otolith size on the stock structure of Mullus barbatus collected from the Bizerte and Ghar El Melh lagoons located in northeastern Tunisia and to evaluate the relationship between the otolith mass asymmetry (OMA) and total length (TL). Analysis of the otolith shape showed a statistically significant intersexual shape difference, i.e. asymmetry, in the left and right and left-left and right-right otoliths between populations of the two lagoons. In addition, significant intersexual differences were detected in Lo, Wo, and Mo, as well as in FA, between the left and right otoliths among the two populations. Moreover, no statistically significant relationship (P > 0.05) was found between OMA and TL between and within the two populations. At the intrapopulation level, a significant intrasexual asymmetry was observed in the left and right, as well as on left-left and right-right sides, otoliths’ shape and size only within the Ghar El Melh lagoon. Discriminant function analysis of the otoliths’ contour shape confirmed the presence of two separate stocks representing the Bizerte and Ghar El Melh lagoons, which should be managed separately. This significant inter and intrapopulation asymmetry detected in otolith shape and size due to FA can be attributed to the instability of larval development caused either by environmental stress associated with variation in water temperature, salinity, feeding conditions and pollutants or due to poor living conditions of larvae resulting from unfavourable environments.

KEYWORDS:

• Elliptical Fourier analysis
• fluctuating asymmetry
• Mullus barbatus
• otolith mass asymmetry
• otolith shape and size
• Tunisia

Acknowledgements

We would like to thank all the people and fishermen who helped us collect the M. barbatus individuals from the two lagoons, the Bizerte and Ghar El Melh. We also thank the anonymous reviewers for their very informative and helpful comments that improved the manuscript.

Animal ethics statement

Specimens for this study were obtained from the catches of licensed fishermen according to the Law of Fisheries and Aquaculture Resources Investment and Protection in Tunisian waters. This study complied with all ethical requirements in Tunisian animal welfare laws and guidelines (No. 1474 certificated on August 14th, 1995). No experiments were conducted on live animals.

Authors’ contributions

Conceptualization, methodology, formal analysis: SBM and MM; validation: AC, MT and ABR; writing-original draft: SBM; writing-review and editing the final manuscript: ABS; supervision and writing-review: JPQ, MT and ABR. All authors read and approved the final manuscript.

Data availability statement

The data that support this study will be shared upon reasonable request to the corresponding author.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors declare that this work has not received external funding from any foundation or organization.