Dietary Ferrous Sulfate Enhances Resistance to -Induced Skin Ulceration in via Immune and Antioxidant Modulation.

The sea cucumber () is a commercially important marine species. However, its survival is increasingly threatened by frequent outbreaks of Skin Ulceration Syndrome caused by . This study evaluated the effects of dietary supplementation with ferrous sulfate (FeSO) at two concentrations (0.5% and 1%) over short-term (21 days) and long-term (56 days) feeding periods on immune defense, antioxidant capacity, and resistance to infection. Key parameters measured included survival rate, cellular immune activity, antioxidant enzyme levels, and expression of immune-related genes. Long-term (56 days) supplementation with 1% FeSO significantly improved survival after infection (90 ± 4.7%). Phagocytic activity and respiratory burst were enhanced by approximately 1.9-fold and ~1.8-fold, respectively ( < 0.05). The expression of , , and genes was upregulated by ~2.1-fold, ~2.0-fold, and ~1.6-fold, respectively ( < 0.05). These results indicate strengthened cellular immunity and antioxidant capacity. Long-term (56 days) supplementation with 0.5% FeSO increased lysozyme activity (1.3-fold) and expression (~4-fold) ( < 0.05), thereby enhancing humoral immunity. In contrast, short-term (21 days) supplementation increased ACP and AKP activities by approximately ~2-fold each, and LZM activity by ~1.2-fold ( < 0.05). However, it did not significantly improve survival, indicating limited protective effects. Overall, 56-day dietary supplementation with FeSO, particularly at 1%, effectively enhances immune and antioxidant responses in This supplementation represents a promising strategy for preventing -induced skin ulceration in aquaculture.