Does Personality Modulate the Sensitivity to Contaminants? A Case Study with Cadmium and Caffeine

Personality has been reported to influence fish response to stress. This study aimed to assess whether shy and bold fish display different sensitivities to two environmental contaminants: caffeine (CAF) and cadmium (Cd). Thus, the sensitivity to Cd was compared based on lethal concentrations (LCs). The potential different response to CAF, known to alter the social behavior and locomotor activity of zebrafish, was studied using behavioral parameters. Overall, different LC values were found for each group: 48 h LC₅₀ values of 4.79 (shy fish) and 8.20 mg·L^-1 (bold fish); and 96 h LC₅₀ values of 3.79 (shy fish) and 9.79 mg·L^-1 (bold fish). In terms of response to CAF, a significant interaction between CAF and personality traits (bold and shy) was found in the locomotion activities (distance travelled, and medium and rapid movements), in the mirror test (frequency of contact and entries into the contact, approach, and distant zones), and in social tests (swimming distance in zones 2 and 3; time spent in zones 1, 2, and 3; and number of entries into zones 1 and 2). Shy fish exposed to 300 μg·L^-1 of CAF presented hypoactivity, reduced aggressive behavior, and reduced sociability. Conversely, CAF did not influence the behavior of bold fish. In general, shy fish were more sensitive to Cd and exhibited anxious behavior when exposed to CAF, which appears to be the factor responsible for changes in their social behavior. Our results highlight the importance of taking personality traits into account in future studies, as variations in behavioral responses between bold and shy individuals can mask the toxicological effects of different chemicals.