Abstract
Hepatopancreatic necrosis syndrome (HPNS) has recently become a major epidemic in shrimp farms, resulting in enormous economic loss. However, its etiology remains controversial. Diseased Litopenaeus vannamei (L. vannamei), collected from shrimp farms, were analyzed for pathological diagnosis, bacterial isolation, and identification. After that, the effects of the three plant extracts on the primary pathogens of HPNS were analyzed in vitro and in vivo. The results revealed that the primary pathogens of HPNS were Vibrio parahaemolyticus (V. parahaemolyticus) with ToxR and TLH gene, V. cholerae with ompW gene, and Proteus vulgaris (P. vulgaris) with rpoA gene. These three bacterial strains exhibited extensive antibiotic resistance. The “Chaiyinhugan” mixture, the “Sanhuanglian” mixture, and the Polygonum hydropiper flavonoid extract inhibited the growth of all three dominant strains. Additionally, the three plant extracts reduced HPNS shrimp mortality, improved shrimp immunity, and attenuated hepatopancreatic pathology. Among them, the Polygonum hydropiper flavonoid extract displayed better effects and could be applied to prevent and treat HPNS in producing and breeding L. vannamei. In conclusion, V. parahaemolyticus, V. cholerae, and P. vulgaris are the major pathogens causing HPNS. Herbal extracts such as Polygonum hydropiper flavonoid extract can be applied to prevent and treat HPNS.