Effects of Temperature on the Antipredator Behaviour and on the Cholinergic Expression in the European Sea Bass (Dicentrarchus labrax L.) Juveniles

In this paper, an experimental approach was used to test for the parallel effects of temperature (T) increase on the antipredator behaviour and the cholinergic expression in the juvenile European sea bass (Dicentrarchus labrax L.). The effects of three T treatments (18, 22 and 26 degrees C) were tested on the main behavioural components of the antipredator response towards live aquatic predators and aerial simulated attacks, whereas brain cholinergic expression was evaluated by choline acetyltransferase (ChAT) immunoblotting (Western blot) at the extreme values of the thermal range (18 and 26 degrees C). Antipredator responses towards a live fish were analysed over pre-exposure and exposure phases within a short temporal scale (20s before and after the stimulus). The results suggest that T modulates several quantitative components of the antipredator behaviour. The mean shoaling index (shoal cohesiveness) was higher at 22 degrees C than at 18 and 26 degrees C during both the pre-stimulus and the exposure phase. Conversely, the mean distances from the predator and the tank bottom were, respectively, lower and higher at 26 degrees C than in the other two treatments. In regard to the antipredator response on the aerial stimulus, comparisons across treatments revealed statistically significant differences between fish performing freezing or latency to recovery, suggesting that the fright reaction has a higher persistence at the coldest T (18 degrees C) than at 22 and 26 degrees C. Western blot analysis revealed a reduction in brain ChAT expression in fish acclimated to 26 degrees C compared to those at 18 degrees C. Results were discussed in the light of the relationships between behavioural traits, metabolism and their consequences on the population level, as a response to climate change in coastal habitats.