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Although otoliths are widely used as archives to infer life‐history traits and habitat use in fishes, their biomineralization process remains poorly understood. This lack of knowledge is problematic as it can lead to misinterpretation of the different types of signals (e.g., optical or chemical) that provide basic data for research in fish ecology, fisheries management, and species conservation. Otolith calcification relies on a complex system involving a pericrystalline fluid, the endolymph, whose organic and inorganic compositions are spatially heterogeneous for some constituents. This property stems from the particular structure of the calcifying saccular epithelium. In this study, we explored the spatial heterogeneity of elemental incorporation in otoliths for two species of high economic interest, European hake Merluccius merluccius (L. 1758) and European sea bass Dicentrarchus labrax (L. 1758). Two‐dimensional mappings of chemical elements were obtained using UV high‐repetition‐rate femtosecond laser ablation (fs‐LA) system coupled to a high‐resolution inductively coupled plasma sector field mass spectrometer analyses on transverse sections of sagittae. Results highlighted a clear asymmetry between proximal (sulcus) and distal (antisulcus) concentrations for elements such as magnesium (Mg), phosphorus (P), manganese (Mn), and potassium (K) with concentration gradient directions that varied depending on the element. Strontium (Sr) and barium (Ba) did not show a proximo‐distal gradient. These results are discussed in light of current knowledge on the endolymph composition and the mechanisms that lead to its compartmentalization, highlighting the need for further research on otolith biomineralization. Operational implications for studies based on otolith chemical composition are also discussed with emphasis on advice for sampling strategies to avoid analytical biases and the need for in‐depth analyses of analytical settings before comparing otolith signatures between species or geographical areas. [ABSTRACT FROM AUTHOR]

All native fishes living in the Caribbean island rivers are considered diadromous but few species have been validated as diadromous. In Guadeloupe (Lesser Antilles) as well as in the other tropical islands, the riverine habitats are subject to strong anthropogenic pressure due to resource modifications or dams. The management of fish biodiversity requires knowledge concerning their life history traits and behaviour that are still unknown for most species at a local scale and at the whole distribution area of the species. In a Guadeloupe river, we inferred the migratory patterns of four freshwater fishes common to Caribbean rivers by the analysis of otolith microchemistry. We found two species Eleotris perniger (Eleotridae) and Sicydium plumieri (Gobiidae) to be completely amphidromous with a marine larval phase and a freshwater adult phase. Agonostomus monticola (Mugilidae) was also found to be amphidromous in this system. The fourth species Gobiesox cephalus (Gobiesocidae) showed elemental ratios suggesting an estuarine larval phase and was defined as "limited amphidromous". The identification of such life history traits, with limited dispersion abilities, argues for specific management measures in tropical island rivers at a basin scale for the conservation of biodiversity. [ABSTRACT FROM AUTHOR]

The amphidromous life cycle and morphological characteristics of Sicydiinae species allow them to colonise tropical freshwater habitats from the river mouth to the upper reaches of the river basin. Otolith microchemistry of 62 Sicydium punctatum from the Pérou River, Guadeloupe (French West Indies) was investigated with a femtosecond laser ablation-inductively coupled plasma mass spectrometer (fs-LA-ICP-MS) in order to reconstruct individual life history and follow the possible movements of Sicydium punctatum after the recruitment. Sr:Ca fingerprint confirmed the amphidromous cycle of this species. Variations of Ba:Ca in some individuals indicated changes in environmental conditions after the recruitment in the river. Even if results did not allow concluding to the specific origin of these variations, the hydrological regime and the biofilm composition may have a non negligible influence on the Ba availability. Results supported the use of multi-elemental signatures in otoliths and highlight the need for a large geographical and temporal sampling of Ba and Sr in freshwater systems for a better understanding of amphidromous fish species. [ABSTRACT FROM PUBLISHER]