The spatial and temporal heterogeneity of rivers largely determine both the richness and the variability of the fish assemblages; however, few studies have been carried out in the northern parts of Mexico. This study assesses the species diversity and longitudinal distribution of fish fauna in the Soto La Marina River (northeast Mexico) and how this relates to environmental variables in an area of biogeographic transition of the Nearctic and Neotropical regions. A total of 89 species (82 natives and seven exotic) belonging to 67 genera and 39 families were recorded. The fish fauna in this basin shows a clear biotic zonation represented by three different species assemblages related to the three physiographic zones of the river (mouth, plain, and mountain) with a replacement of species throughout a temperature and salinity gradient. A principal component analysis found that Astyanax mexicanus, Poecilia mexicana, and Herichthys cyanoguttatus were the most abundant species in the plain and mountain zones of the river but exhibited different high abundance hotspots throughout the basin. Salinity, conductivity, and total dissolved solids increased downstream, directly impacting fish composition and diversity. The mouth of the river was characterised by high salinity and conductivity values correlating with high species richness of marine derivation. Similarly, the richness of species negatively correlated with the longitudinal gradient of the river. An integral knowledge of the relationship between environmental and anthropogenic parameters in the Soto La Marina River basin will enable the design of conservation and management strategies for its fish resources and habitats.

河流的时空异质性在很大程度上决定了鱼类群落的丰富性和变异性；然而，在墨西哥北部地区开展的研究很少。本研究评估了索托拉马里纳河（墨西哥东北部）鱼类群的物种多样性和纵向分布，以及这与近北和新热带地区生物地理过渡区域的环境变量之间的关系。共记录了属于 67 属 39 科的 89 种（82 种本地物种和 7 种外来物种）。该盆地中的鱼类群显示出清晰的生物区带，由与河流的三个自然地理区（河口、平原和山地）相关的三种不同物种组合代表，并在整个温度和盐度梯度中更换物种。Astyanax mexicanus , Poecilia mexicana和Herichthys cyanoguttatus是河流平原和山区最丰富的物种，但在整个盆地表现出不同的高丰度热点。下游的盐度、电导率和总溶解固体增加，直接影响鱼类的组成和多样性。河口的特点是高盐度和高电导率值与海洋衍生的高物种丰富度相关。同样，物种丰富度与河流的纵向梯度呈负相关。全面了解 Soto La Marina 河流域环境和人为参数之间的关系，将有助于为其鱼类资源和栖息地设计保护和管理战略。