Efficacy of Rose Myrtle Rhodomyrtus tomentosa Seed Extract against Acute Hepatopancreatic Necrosis Disease in Pacific Whiteleg Shrimp Penaeus vannamei.

Acute hepatopancreatic necrosis disease (AHPND) is a new emerging bacterial disease that has been recently reported to cause mass mortalities in Pacific whiteleg shrimp Penaeus vannamei. Antibiotics have been used to treat bacterial diseases in shrimp, but most of them have been ineffective and have resulted in drug residues in the harvested shrimp products. In this study, an alternative approach was tested for its efficacy in controlling AHPND. The extract of rose myrtle Rhodomyrtus tomentosa seed, a traditional Vietnamese medicine, was tested for antibacterial effect against three AHPND bacterial strains in vitro (Vibrio parahaemolyticus [VP_AHPND ] KC12.020, VP_AHPND KC13.14.2, and V. harveyi KC13.17.5) and was further evaluated for its potential efficacy in prevention of AHPND in shrimp in vivo. The in vitro studies showed that the antibacterial activity of the R. tomentosa extract was dose dependent, with the strongest bacterial susceptibility (≥18.0 mm) at a concentration of around 3,500 μg/disc. The in vivo studies showed that after challenge with VP_AHPND KC12.020, the survival rates for shrimp in the groups that received feed pellets supplemented with extract at 3.5% or 7.0% (survival ~48.9% and 52.2%, respectively) were significantly higher than the zero survival rate in the positive control group, which received feed without the extract. These results indicate that the use of the R. tomentosa extract as an alternative therapy for control of AHPND in shrimp could help to minimize disease outbreaks. As a result, the extract is further expected to reduce drug/chemical residues in shrimp products.