Functional and molecular immune responses in Octopus vulgaris skin mucus and haemolymph under stressful conditions

The common octopus (Octopus vulgaris) is a cephalopod species with a high economic market value, hence one of the species in spotlight to be reared in aquaculture. The increasing importance of animal welfare has ethical considerations and also implications for improving quality standards. Unfortunately, defence mechanisms in cephalopods are largely unexplored and a comprehensive insight on cephalopod physiological and immune responses in relation to stress becomes particularly prominent. Therefore, the aim of the present study was to gather deeper insights on functional and molecular stress biomarkers in the common octopus. For this purpose, adult individuals were exposed to a stressful condition by limiting movements in the aquarium for 17 days. Innate immune parameters were assessed in skin mucus and plasma samples whereas the expression level of genes coding for antioxidant enzymes, related to immune functions, or involved in folding proteins was analysed in haemocytes at several sampling times. Our results indicated that most of the innate immune parameters measured (haemolytic, lysozyme, esterase, peroxidase, and protease activities) in skin mucus showed substantial variations at middle term of experiment (i.e., 11 days). After 11 days of movement limitations, the haemolytic and protease activities decreased in the octopus plasma. At the transcriptional level, lyz, hsp90 and ire1 gene expression values were particularly down-regulated while C1-like, prdx and sod transcripts showed up-regulation over an early stage (i.e., 5 days) in haemocytes from octopuses under stressful conditions. Moreover, C1-like, prdx and sod mRNA expression decreased at 11 and 17 days whereas lyz and hsp90 gene expression level augmented at 11 days in exposed octopus compared to unexposed specimens, with the subsequent increase at plasma and skin mucus level at long term. Overall, results from the present study showed potential functional and molecular biomarkers which could be of assistance in studies comprising stressful conditions in the common octopus. Moreover, biomarkers from skin mucus could also be considered as a low-invasive approach to assess and improve cephalopods welfare.