Abstract
Introduction: Otoliths have been widely used in recent years as tracers of fish life history, ranging from visual aging to chemical analyses that reconstruct environmental conditions, migration patterns, and metabolic changes. Yet, Iberian endemic or endangered species are understudied. This study focuses on Andalusian barbel (Luciobarbus sclateri), endemic to the southern half of the Iberian Peninsula. Objective: The aim was to evaluate whether otolith chemical profiles can simultaneously support age estimation and reveal the impact of environmental variations, particularly hypoxia. Methodology: Fish were caught in two sites with different environmental properties, including strong hypoxia: the Guadalquivir estuary and the dock of Seville (which is isolated from the main river channel by a ship lock and could, therefore, be used as a control). Otolith chemical composition was analyzed from core-to-edge transects with a laser-inductively coupled plasma mass spectrometer (LA ICP-MS). Results: Patterns of variation in Mg and Mn in relation to hypoxia and environmental conditions are discussed. We visually counted growth rings in the sections, and we found a strong correlation (R2 = 0.904) in Mg:Ca peaks with growth rings. Body condition, assessed using Fulton’s condition factor (K), differed between sites, with fish from the estuary exhibiting a lower condition than those from the dock. Conclusions: The strong correlation between counter growth rings and Mg:Ca peaks suggests that chemical analysis could be used as a valid method for supporting aging. The pattern of lower condition in fish from the estuary is consistent with persistent hypoxic events documented in the estuary but not within the dock environment. This whole approach provides a powerful framework to assess habitat quality and support conservation of L. sclateri in the Guadalquivir estuary.
Author Contributions
Conceptualization, J.M.-G., J.M.M., P.R.-S. and C.M.; methodology, J.M.-G., J.M.M. and P.R.-S.; validation, J.M.-G., J.M.M. and P.R.-S.; formal analysis, J.M.-G., J.M.M. and P.R.-S.; investigation, J.M.-G.; resources, P.R.-S., C.M., B.M.G. and J.C.G.-G.; data curation, J.M.-G., J.M.M. and P.R.-S.; writing—original draft preparation, J.M.-G.; writing—review and editing, J.M.M., P.R.-S. and C.M.; visualization, J.M.-G.; supervision, J.M.M.; project administration, J.M.M. and C.M.; funding acquisition, J.C.G.-G. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the University of Seville (US) and the Authority Port of Seville (APS). The presenting author acknowledges the financial support provided by the Gasterosteus Fund of the Iberian Society of Ichthyology (SIBIC) through the Gasterosteus Grant covering the SIBIC 2026 Congress registration fee.
Institutional Review Board Statement
The animal study protocol was approved by the Institutional Review Board of Junta de Andalucía (JA).
Informed Consent Statement
Not applicable.
Data Availability Statement
Available upon request.
Conflicts of Interest
The authors declare no conflicts of interest.
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