Global Patterns and Gaps in Research on Salinity Tolerance of Inland Fishes

ABSTRACT Freshwater salinization is an emerging threat impacting approximately one‐third of the world's freshwater bodies. However, the salinity tolerance of many inland fishes remains understudied, despite being a crucial factor in determining species distributions and fitness. We updated and analysed a comprehensive global database of experimental salinity tolerance, compiled from 128 sources, to investigate geographical and taxonomic biases in research on the salinity tolerance of inland fishes. Additionally, we examined how salinity tolerance relates to fish traits and how experimental data align with field‐reported salinity levels. Experimental data on salinity tolerance was available for < 1% of the world's inland fishes, with data severely lacking from diverse tropical regions and species‐rich orders such as Characiformes and Siluriformes. Most salinity tolerance studies focused on relatively large and widely distributed species from North America, Europe and Oceania and certain orders such as Acipenseriformes, Centrarchiformes, Cyprinodontiformes or Lepisosteiformes. Our results showed that fish salinity tolerance was strongly associated with fish habitat type, taxonomy, aspects of morphology, migratory behaviour and the experimental approach used (direct vs. gradual). Our results also showed significant, though sometimes weak relationships between field‐reported salinity levels and experimental estimates. Improved understanding of fish salinity tolerance will be essential for assessing impacts of freshwater salinization and forecasting the invasion potential of non‐native species.