Antimicrobial Activities and Immune Responses of Methanolic Extract of Najas indica on Shrimp (Penaeus Monodon)

Abstract

The aim of this study was to evaluate the influence of Najas indica on the immune system and health of shrimp. Antibacterial activity, immune parameters, and a challenge experiment against White Spot Syndrome Virus (WSSV) were assessed. The results revealed that the methanolic extract of Najas indica exhibited significant antibacterial activity with 15±2 mm inhibition zone, indicating its potential as an antimicrobial agent. Furthermore, shrimp fed with a 1 mg/kg methanol extract of Najas indica displayed significantly increased levels of Total Hemocyte Count (51.73 ± 2.25×105) cells/ml and Superoxide Dismutase (SOD) activity (4.3 ± 0.72 U/mg) compared to other treatments, suggesting enhanced immune response and oxidative stress defense. Significant differences were observed in the clotting times of shrimp hemolymph collected from individuals fed with 1 mg/kg Najas indica extract compared to other treatments. Notably, the clotting time was the shortest (3.67 s) in the 1 mg/kg treatment, indicating improved coagulation response. Conversely, the control group (without Najas indica extract) exhibited the longest clotting time (10.67 s). In the challenge experiment against WSSV, shrimp fed with Najas indica extract (1 mg/kg) showed reduced mortality compared to the control group. Probit analysis determined the LC50, and the control group exhibited significantly faster mortality rates than the treatment group. The cumulative hazard probability of shrimp mortality was lower in the treatment group than in the control group. In conclusion, this study demonstrated that extracts from Najas indica possess therapeutic effects and may serve as a potential natural medicine for aquatic animals, specifically in shrimp health management.