Identification of Fusarium solani as a causal agent of black spot disease (BSD) of Pacific white shrimp, Penaeus vannamei

In Nov 2020, mass mortality of cultured Pacific white shrimp (Penaeus vannamei) occurred due to black spot disease (BSD) in some shrimp farms in China. To investigate the disease cause, a potential pathogenic fungus was isolated from melanized lesions of P. vannamei suffering from the BSD syndrome. The fungal isolate was then identified as Fusarium solani based on TEFla and ITS-gene sequences. The isolate of fungus was used in infection studies. This study used Koch postulates confirmed that the studied agent was causing BSD symptoms in the white leg shrimp, which were significantly symptoms relieved after molting. Results showed that an identical fungus was re-isolated from black lesions after the artificial infection period. Virulence test revealed that F. solani could cause 88.66% mortality within 30 dpi at a dose of 1.02 x 10(6) CFU/mL, and the LC50 of F. solani at 30 dpi is 3.37 x 10(4) CFU/mL. The accumulative mortalities also displayed concentration dependence. The histopathological characterization displayed that responses of P. vannamei against F. solani are haemocytic infiltration, encapsulation, melanization, etc. in the black spot lesions. Furthermore, severe infection of F. solani in P. vannamei causes molting failure, and further contributes to the mortality of the diseased individuals. The findings of our study would be useful to provide a theoretical basis for early prevention and control of BSD.