Investigating Depressive-Like States in Crayfish (Procambarus alleni) through Unpredictable Chronic Mild Stress
Résumé
Crustaceans are now intensively farmed in many fields, including aquaculture or research, and laws to protect them have been implemented since 1998 in countries such as Australia, New-Zealand, Italy, Switzerland and Austria. Recently, a proposal safeguarding those species during transportation has been adopted by the European Commission. The necessity to expand our knowledge concerning the physiological and ethological needs of crustaceans has become increasingly important to improve the welfare and well-being of these animals. Indeed, meeting these needs allow to induce positive mental and physical state in animals. Nevertheless, the emotional states of the crustaceans remain barely understood. Studies have shown that crayfish can exhibit anxiety-like behaviours, naturally during moult- ing or after an acute stress exposure. During these stressful events, crayfish are more likely to avoid dangerous situations, which may enhance their survival and overall fitness . We however hypothesise that, during prolonged stress exposure, further neurobehavioural al- terations could be taking place, such as depressive-like states which may be reminiscent of depressive disorders analogous of those observed in mammals. To investigate whether chronic stress exposure could indeed induce such states in crustaceans, we are adapting a well-established vertebrate protocol - Unpredictable Chronic Mild Stress - to the crayfish Procambarus alleni, aligning it with the specific needs and behaviours of this species. Animals are randomly exposed to mild stressors several times per day over several weeks to induce depressive state in this procedure. Then, in order to validate this state, key behavioural changes such as anxiety, social behaviour, anti-predatory responses, decision-making, and daily activity budget are evaluated . Further analysis of the neuro- physiological mechanisms underlying depression should confirm our behavioural observations by measuring physiological markers of inflammation, of stress (glucocorticoids, glucose) and brain serotonin level. All these results would provide criteria for monitoring the welfare of crayfish, a better un- derstanding of their emotional states and to discuss of the phylogeny and the adaptive value of the depressive-like behaviours.