Linking Life History Traits to the Threat Level of European Freshwater Fish

Over 40% of freshwater fish species in Europe are currently at risk of extinction, highlighting the need for improved conservation planning. This study examines whether the threat status is associated with life-history and ecological traits across 580 autochthonous (native and endemic) freshwater fish species in European inland waters. Using data from FishBase and the IUCN Red List, we assessed associations between threat level and both categorical (e.g., migratory behavior, commercial importance, reproductive guild, and body shape) and numerical traits (e.g., maximum length, weight, age, growth parameters, and maturity traits). Significant, though modest, associations were identified between species threat level and migratory behavior and reproductive guild. Non-migratory species exhibited higher median threat levels, while amphidromous species showed a non-significant trend toward higher threat, suggesting that limited dispersal ability and dependence on fragmented freshwater networks may increase extinction vulnerability. Species with unclassified reproductive strategies also showed elevated threat levels, possibly reflecting both actual risk and underlying data gaps. In contrast, body shape and trophic level were not significantly associated with threat status. Critically Endangered species tend to be larger, heavier, and mature later—traits characteristic of slow life history strategies that limit population recovery. Although length at maturity and maximum age did not differ significantly among IUCN categories, age at maturity was significantly higher in more threatened species, and growth rate (K) was negatively correlated with threat level. Together, these patterns suggest that slower-growing, later-maturing species face elevated extinction risk. Overall, the findings underscore that the threat level in European freshwater fish is shaped by complex interactions between intrinsic biological traits and external pressures. Trait-based approaches can enhance extinction risk assessments and conservation prioritization, especially in data-deficient freshwater ecosystems facing multifaceted environmental challenges.