Biomarker-based assessment of somatostatin-6 immunomodulation in gilthead seabream: From serum proteins to skin mucus enzymes.

This study evaluated the immunomodulatory role of somatostatin-6 (SST6) in gilthead seabream (Sparus aurata) using a validated inflammation model induced by λ-carrageenan and a comprehensive panel of serum and skin mucus biomarkers. SST6 was administered at 1 nM and 2 nM, and its effects were assessed in these matrices. In fish injected with SST6 alone, serum alternative complement activity increased at both concentrations. In skin mucus, λ-carrageenan reduced peroxidase, esterase, and protease activities, whereas SST6 administration was associated with lower non-Ig protein levels and reduced peroxidase, esterase, and protease activities. When combined with λ-carrageenan, SST6 at 1 nM increased serum immunoglobulin levels and α2-globulins in the proteinogram fractions, while further decreasing the oxidative and proteolytic activities in skin mucus. Correlation analysis revealed the coordinated regulation of key mucosal enzymes, reinforcing the functional integration of local immune responses. These results indicate that SST6 is able to modulate systemic and mucosal humoral biomarkers. Furthermore, this study provides the first evidence of complement activation by SST6 in fish and highlights the value of integrating biomarker-based tools to monitor immunophysiological responses and test bioactive compounds in aquaculture research.