Dietary Supplementation with Cyanobacterium Oscillatoria limnetica Modulates Growth Performance and Disease Resistance in White-Leg Shrimp, Litopenaeus vannamei

This research investigates the effects of incorporating cyanobacterium Oscillatoria limnetica (OL) powder into aquafeeds on the growth rates, activity of digestive enzymes, antioxidant status, and innate immune responses of white-leg shrimp, Litopenaeus vannamei. The shrimps’ resistance against possible infection with Vibrio harveyi was also examined. For 12 weeks, shrimps (1.26 ± 0.088 g) were nourished on experimental diets with 0.0, 0.75, 1.5, 2.25, and 3.0 g OL/kg feed, represented as OL0, OL0.75, OL1.5, OL2.25, and OL3.0, respectively. At the end of the feeding trial, shrimps were challenged by V. harveyi, and their mortality was further observed for further ten days. The shrimps fed on OL-enriched diets, particularly OL3.0, showed significantly greater growth, digestive enzyme activities, and innate immunity performance than those fed on the control diet (OL0). Compared to the control group, enzymatic antioxidant parameters (CAT and SOD) were significantly (p < 0.05) higher; meanwhile, MDA levels showed marked declines in shrimps fed on OL-containing diets (particularly OL3.0). The relative mRNA expression of antioxidant-related genes (cMn-SOD, CAT, and GPx) and immune-related genes (HMC, Alpha2M, ProPO, and Pen3a) was upregulated in the OL-fed animals compared to the control group. The intestinal morphometry was markedly enhanced in the animals fed on OL-enriched diets, especially with respect to the OL3.0 diet. After the bacterial challenge assay against V. harveyi for ten days, shrimps fed on the control diet had 83.3% mortality; meanwhile, the mortality rate was lower in shrimp groups fed on OL diets, particularly OL3.0 (46.7%). This study demonstrates that L. vannamei benefits from dietary inclusion of O. limnetica (3.0 g/kg feed) through accelerating its growth due to better digestion of diets. Additionally, the OL meal acts as a functional ingredient that fortifies the shrimp against possible V. harveyi infection by enhancing their biological defense system.