Effect of altitudinal gradient on reproductive and feeding behaviours of four congeneric endemic freshwater fish in the Zat Catchment (Morocco)

Abstract

The adaptive capacity of freshwater fish enables them to undergo morphological and structural changes in response to environmental fluctuations. Documenting these responses is crucial to assess species vulnerability to ecological perturbations. This study investigated the reproductive, feeding and physiological adaptations of four endemic fish species (Luciobarbus ksibi, Carasobarbus fritschii, Atlantor reinii and Luciobarbus magniatlantis) across an altitudinal gradient (690–1570 m) in Moroccan river catchment areas in 2023. Field sampling targeted a range of key biological and statistical indicators utilising 129 specimens. Gonadosomatic Index (GSI) and Viscerosomatic Index (VSI) analyses revealed significant variations driven by altitude, species and sex, with L. ksibi consistently exhibiting the highest values across gradients, indicating its superior reproductive and energy allocation strategies. Scaled mass index (SMI) further demonstrated distinct interspecies and altitudinal patterns, with marked differences in smaller size classes at higher altitudes. Total weight, digestive tube weight and gonad weight were key drivers of physiological differentiation, with species and altitude emerging as the dominant factors influencing variability. These insights are essential for informing conservation efforts and understanding the impacts of climate change on freshwater ecosystems.