Abstract
Introduction: The Catalan chub (Squalius laietanus) is a freshwater cyprinid endemic to Catalonia, from the lower course of the Ebro River to the Tech, Tet, Agly, and Massane rivers in France. Classified as Vulnerable in the IUCN Red List (2024), its populations face significant threats due to anthropogenic pressures and the potential hybridization with the European chub (Squalius cephalus). Objective: This study aimed to characterize the genetic variation of the mitochondrial control region (CR) of S. laietanus across the main Catalan river basins to determine the population genetic structure of this species in the core of its distribution range. Methodology: A 789 bp fragment of the CR was sequenced in 334 chubs from 24 sampling sites collected by electrofishing between 2021 and 2025. The S. laietanus specific matrilineage of all these specimens had been previously detected by sequencing the Cytochrome c oxidase subunit I (COI) but this marker did not detect clear genetic structuring among basins. Results: In contrast to the low diversity within and among locations reported by COI, the CR showed a population structure distinguishing between northern (Muga, Fluvià, Daró, Ter, and Tordera rivers) and southern basins (Besòs, Llobregat, Gaià, Francolí, and Ebro rivers). In the southern rivers, a single haplotype, (H1), was present. This haplotype declined in abundance towards the north, being replaced with H2. In the Muga River, native Catalan chub populations showed the fixed H3 haplotype, suggesting strong isolation, while populations from the Daró River contained a private haplotype (H4). In contrast, the presence of a common and single haplotype in southern basins possibly resulted from genetic drift under strong summer droughts. Conclusions: Overall, these results reveal population structuring in S. laietanus and highlight the importance of considering regional differentiation in conservation and management strategies.
Author Contributions
Conceptualization, S.H., J.-L.G.-M., and A.A.; methodology, N.P.-B., L.W., and H.M.; software, N.P.-B., L.W., H.M., S.H., J.-L.G.-M., and A.A.; investigation, N.P.-B., S.H., J.-L.G.-M., and A.A.; writing—original draft preparation, N.P.-B.; writing—review and editing, N.P.-B., S.H., J.-L.G.-M., and A.A.; supervision, S.H., J.-L.G.-M., and A.A.; project administration, S.H., J.-L.G.-M., and A.A.; funding acquisition, S.H., J.-L.G.-M., and A.A. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by contract AG-2021-686 of the Inland Fisheries Services of the Autonomous Government of Catalonia (Servei de Pesca Continental, Departament d’Agricultura, Ramaderia, Pesca i Alimentació, Generalitat de Catalunya) and received a grant (IEC-PR2025-3-REC) from the IEC within the framework of the call for research grants 2025. The APC was funded by AWY.
Institutional Review Board Statement
Not aplicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data presented in this study will be made available by the authors on request.
Conflicts of Interest
The authors declare no conflicts of interest.
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