Cannibalism is linked to exploratory trait in perch Perca fluviatilis larvae.

Cannibalism is a major source of mortality in the early rearing phases of many fish species, among which Eurasian perch (Perca fluviatilis). Even though several studies highlighted the importance of both morphological traits and environmental conditions in shaping cannibalistic behaviour, the role of individual behavioural variation - particularly consistent traits associated with animal personality - remains largely unexplored. In this study, we assessed whether perch larvae identified as cannibals differed from their non-cannibal congeners for behavioural traits such as exploration, activity, boldness (latency to emerge), and shoaling tendency. Behavioural assays were conducted twice for each individual, allowing assessing trait repeatability. Morphological measurements (total length, mass, head size, and mouth dimensions) were also recorded. Principal component analysis revealed that exploration, activity, shoaling tendency, and age were positively correlated and opposed to shyness. Behavioural traits showed moderate repeatability after controlling for age, particularly for exploration, boldness, and shoaling; activity was highly influenced by age, but it was not repeatable. Comparison between cannibals and non-cannibals revealed no consistent differences in behavioural traits, except for lower exploration in cannibals during the first session test. This difference did not persist in the second session, suggesting context-dependent variation rather than fixed personality differences. Morphologically, no significant differences in body size or head/mouth dimensions were found between groups, although trends suggested slightly larger mouth dimensions in cannibals. Our findings suggest that larval cannibalism in Eurasian perch is not strongly associated with neither consistent behavioural nor morphological traits. Rather, it may reflect a plastic, opportunistic strategy influenced by transient internal states (e.g., hunger), environmental conditions such as density, or developmental transitions toward piscivory. This challenges the assumption that personality traits can reliably predict behaviours such as cannibalism in early life stages. Our findings are crucial for optimising larval rearing protocols and improving survival rates in aquaculture. [ABSTRACT FROM AUTHOR]