Seasonal cooling constrains the establishment potential of Macrobrachium rosenbergii in temperate regions

The freshwater prawn Macrobrachium rosenbergii , native to Southeast Asia and widely farmed in tropical regions, is increasingly considered for aquaculture in temperate climates. However, its potential establishment following escape remains uncertain in temperate regions. Although thermal limits under acute stress are relatively well documented, the effects of gradual seasonal temperature changes, which are more representative of natural conditions, remain poorly understood. Here, we assessed the thermal tolerance of M. rosenbergii under both gradual and acute temperature regimes. While individuals tolerated acute cold exposure down to 9 °C, prolonged exposure to gradually decreasing temperatures resulted in mortality at higher thresholds (13 °C), indicating increased sensitivity under realistic seasonal conditions. Similar discrepancies were observed under warming treatments. In addition, gradual thermal stress impaired background colour adaptation, resulting in reduced or even complete loss of pigmentation and potentially increasing vulnerability to visual predators. Thermal tolerance also varied across developmental stages, with post-larvae showing higher lethal temperature to acute stress than adults. These results demonstrate that gradual seasonal cooling, rather than acute thermal extremes, is likely to represent a critical barrier to overwinter survival. Consequently, the establishment of M. rosenbergii in temperate freshwater systems appears unlikely in regions where winter temperatures fall below this threshold. This study highlights the importance of incorporating realistic environmental dynamics when assessing invasion risk and identifies seasonal temperature variation as a key bottleneck in the invasion process.