Short-term swimming up-regulates pro-inflammatory mediators and cytokines in gilthead seabream (Sparus aurata)

Aerobic swimming exercise in fish has been shown to improve robustness of some species. However, the optimal conditions to be applied and the mechanisms underlying remain unknown. We investigated the effects of 6 h of induced swimming on the immune response of gilthead seabream (Sparus aurata), by analysing markers related to immune status in plasma, skin mucus, gills, heart and head-kidney. Forty fish were individually exercised in swim tunnels by applying different water currents: steady low (SL, 0.8 body lengths (BL) s−1), steady high (SH, 2.3 BL s−1), oscillating low (OL, 0.2/0.8 BL s−1) and oscillating high (OH, 0.8/2.3 BL s−1) velocities, including a non-exercised group with minimal water flow (MF, <0.1 BL s−1). Swimming conditions did not trigger a stress response or anaerobic metabolism, suggested by similar levels of cortisol, lactate, and glucose in plasma among groups. Blood haemoglobin and innate immune parameters in plasma and skin mucus also remained unaltered. However, decreased blood haematocrit was observed in fish swimming on the OL condition. Interestingly, gene expression analysis revealed that the OL condition led to the up-regulation of pro-inflammatory mediators (nfκb1 and mapk3) and cytokines (tnfα, il1β and il6) in gills. A similar response occurred in heart, with an up-regulation of nfκb1, tnfα, il6 and cox2 in the OL condition. Gene expression of these cytokines was unaltered in the head-kidney. The inflammatory response in gills and heart of gilthead seabream triggered by the OL condition highlights the importance of establishing suitable rearing conditions to improve welfare of cultured fish.