Induced swimming in European seabass (Dicentrarchus labrax): effects on the stress response, immune, and antioxidant status.

Suitable swimming conditions can improve the growth and welfare of farmed fish. This study investigated how swimming affects immune and oxidative responses in European seabass (Dicentrarchus labrax), an important farmed fish species in Southern Europe. Thirty-two specimens were assigned into four experimental groups with the following conditions for 6 h: steady low (L, 0.8 body lengths (BL)⋅s^-1); steady high (H, 2.2 BL⋅s^-1); oscillating (O, 0.8-2.2 BL⋅s^-1) swimming speeds; and control non-induced to swim (C, < 0.1 BL⋅s^-1). The H group exhibited higher white blood cell counts and plasma cortisol levels compared to the C and L groups. However, innate immune parameters in plasma and skin mucus showed no differences between groups. Gene expression revealed an up-regulation of inflammatory cytokines (tnfα and il1β) and igf1 in the gills of fish from H and L groups, respectively, whilst no variations were observed in the head-kidney. In the skin, tnfα was up-regulated in the L group. Moreover, the H group showed increased superoxide dismutase and catalase activities and higher lipid peroxidation levels in red muscle. The L group had a higher ratio of reduced/oxidized glutathione (GSH: GSSG) in red muscle, suggesting enhanced antioxidant status. Under all swimming conditions, the GSH: GSSG ratio was increased in the white muscle. Conversely, hepatic markers of oxidative stress were similar among groups. Results suggest that steady swimming at 0.8 BL⋅s^-1 enhanced the antioxidant status in red muscle which may be of relevance to improve the welfare of this cultured species.