Acclimation effect on fish migratory characteristics: determination of appropriate acclimation period for Chinese sturgeon, <scp><i>Acipenser sinensis</i></scp>

The acclimation period is a crucial and controllable factor in managing fish stress prior to behavioural observations. However, research in this area-particularly regarding its effects-remains limited. In the present study, we investigated the effect of acclimation duration (up to 265 min during the day and up to 525 min at night) on the migratory characteristics of juvenile Chinese sturgeon (Acipenser sinensis). The appropriate acclimation period for juvenile Chinese sturgeon was determined based on two observational indicators (migratory speed and activity intensity) and one statistical core (coverage probability). Our results indicate that the appropriate acclimation period was not influenced by the observational indicators or social community relationships (one-tailed vs. group), but was significantly affected by circadian rhythms (day vs. night). Specifically, the minimum acclimation period required for juvenile sturgeon to adjust their activity to a more stable level is 1 h during the day and approximately 3 h at night. These significant circadian differences may be attributed to the physiological stress experienced by the fish due to dark adaptation, suggesting that dark adaptation and acclimation duration are critical for managing fish stress prior to behavioural observations. This study not only clarifies the ecological or anthropogenic factors influencing fish acclimation periods but also establishes a standardized method for determining the acclimation period. Although the behavioural indicators may not be applicable to non-migratory fish, the novel methods and findings provide valuable references for fish acclimation research. Furthermore, this research offers a new solution for standardizing animal behavioural studies, including those involving fish, thereby enhancing the stability and reliability of behavioural data and promoting effective animal stress management.