Boldness associated with higher erythrocyte levels and preference for higher temperatures can support the spread of European catfish to novel and warmer ecosystems

Here, we provide data on hematological, biochemical, and behavioral indices measured in fish during the study. ID – Sample identification number The maze experiment indices listed below were assessed in both maze settings, and their mean was used as the individual characteristic for further computations: Activity_maze – Number of antennae passed Boldness_maze – Time between the start of the experiment and the first detection of an individual by an antenna (transformed into a continuous 0–1 index scale; 0 indicates that individual never entered the maze) Exploration_maze – Time needed to explore the entire maze, i.e., the time between the first and the last antenna detections (transformed into a continuous 0–1 index scale; 0 indicates the individual never explored the entire maze) Preferred temperature_maze – Relative preferred temperature (difference between the temperature in the compartment where the fish was present and the temperature in the central part of the maze, used as a baseline) The field indices listed below are expressed as mean values: Home range_field – Assessed using the minimum convex polygon (MCP) method Activity_field – Movement during a 24-hour cycle, determined as the distance between fish positions at two subsequent 3-hour intervals Preferred temperature_field – Difference between individual sensor temperature and the general river temperature (used as a baseline)