<p>Consistent individual behavioural variation plays a crucial role in shaping ecological interactions and driving evolutionary processes. While laboratory studies assess personality traits under controlled conditions, their ecological validity is uncertain, as behaviour in natural settings is influenced by complex environmental and social factors. Here, we use juvenile Arctic charr to investigate whether traits commonly described as boldness and aggressiveness under laboratory conditions can reliably correlate with corresponding behaviours in natural settings, and if these traits form a behavioural syndrome in the two contexts. Ninety-six juvenile individuals were tagged and tested twice for boldness and aggressiveness in both lab and field settings. In the lab, fish underwent standardised open-field tests, whereas in the field, they were placed in 12 stream enclosures, split evenly between high shelter and low shelter availability treatments. Boldness and aggressiveness were both repeatable within laboratory and field settings. However, there was no correlation within these traits across contexts, nor any evidence of a boldness-aggressiveness behavioural syndrome in either setting. Furthermore, body size, water temperature, and shelter availability influenced aggressiveness in the field. Our findings suggest that the laboratory assays used in this study may not fully capture the specific behaviours we targeted when expressed in more complex, ecologically relevant situations. These results underscore the importance of refining laboratory tests to ensure that they accurately represent the ecological conditions under which personality traits are expressed. Such improvements are essential for drawing reliable conclusions about the role of personality in shaping social status, life history, and fitness, in natural populations.</p>