Aspergillus niger-fermented watermelon rind enhances growth, immunity, and heat stress resilience in Asian seabass ( Lates calcarifer ).

An 8-week feeding study was undertaken to assess the impacts of incorporating yeast-fermented watermelon rind powder (FWRP), produced using Aspergillus niger, on growth performance, antioxidant capacity, immune responses, and thermal stress tolerance in Asian seabass fingerlings. Three hundred fish, averaging 5.68 ± 0.32 g in initial weight, were assigned at random to 12 tanks, with 25 individuals stocked in each tank. The fish received the assigned diets with different FWRP levels of 0.0, 10, 20, and 30 g/kg feed (FWRP0, FWRP10, FWRP20, and FWRP30, respectively) over the course of 8 weeks. At the end of the feeding trial, fish were exposed to thermal stress by increasing water temperature from 23 to 32 °C at 3 °C day⁻¹ and maintaining it at 32 °C for 3 days. The findings showed that the dietary FWRP notably stimulated growth, antioxidant, and serum immune parameters of Asian seabass fingerlings relative to the control group (P < 0.05). Fish fed on 30 g FWRP/kg feed produced the highest values of growth, digestive enzymes, antioxidant, and immune indices. Activities of alkaline phosphatase and aspartate aminotransferase declined as levels of FWRP in diets increased, and their lowest levels were detected in fish fed on FWRP20 and FWRP30. The findings revealed that the use of fermented FWRP may serve as an effective feed additive for Asian seabass, promoting growth performance, enhancing antioxidant and immune responses, and increasing resistance to hyperthermia stress.