Dietary biotin supplementation modulates immune and antioxidant-related responses in the sea cucumber Apostichopus japonicus exposed to Vibrio splendidus.

Skin ulcerative syndrome (SUS), caused mainly by Vibrio splendidus, remains a major constraint on the culture of the sea cucumber Apostichopus japonicus, and effective dietary measures that raise disease resistance are still lacking. Biotin is a promising immunonutrient, but the inclusion level and feeding duration that optimise the immune and antioxidant responses of sea cucumbers have not been established. Here, two feeding trials (21 and 56 days) were conducted with a commercial 1% biotin premix incorporated into the basal diet at 1.0%, 1.5% and 2.0% (approximately 100, 150 and 200 mg/kg biotin, respectively), each followed by a V. splendidus challenge. Supplementation raised survival in every treatment group in both trials, and the magnitude of the cellular immune and antioxidant-related responses was governed by inclusion level and feeding duration. In the short-term trial, the 1.0% and 1.5% biotin premix groups showed significantly higher alkaline phosphatase (AKP), acid phosphatase (ACP) and superoxide dismutase (SOD) activities and significantly higher c3 and sod expression than the control, and the 1.5% premix group reached the highest survival; the cellular immune gains emerged with prolonged feeding. In the long-term trial, the 1.5% biotin premix group showed the highest phagocytic and respiratory burst activities and the strongest upregulation of sod and ferritin, and it again achieved the highest survival, while its AKP and ACP activities did not differ significantly from the control. In both trials, lyz, tlr3 and hsp70 responded in an inclusion-level- and feeding-duration-dependent manner rather than increasing uniformly, and the highest inclusion level, 2.0%, generally gave the weakest responses. Dietary biotin premix at 1.5% therefore modulates immune and antioxidant-related responses in A. japonicus and improves survival after V. splendidus challenge. These results support further evaluation of dietary biotin premix as a sustainable component of disease-management strategies for SUS in sea cucumber aquaculture.