Hepatopancreas color as a phenotype to indicate the infection process of Vibrio parahaemolyticus in Pacific white shrimp Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) is a major bacterial disease of the Pacific white shrimp Lito-penaeus vannamei. An effective phenotype measurement to evaluate disease resistance is crucial for selective breeding of shrimp. However, it is difficult to find a suitable phenotype to evaluate the disease resistance in shrimp, which can be easily measured in a high-throughput manner. The target tissue of AHPND is the hepa-topancreas of shrimp which shows color changes in appearance when AHPND occurs. In the present study, the correlation between the hepatopancreas color and the infection process was analysed to find an easy way to evaluate the resistance of shrimp to AHPND. The infection process of V. parahaemolyticus was divided into three phases: initial stage, acute stage and recovery stage. By observing the hepatopancreas color of shrimp, the hepatopancreas could be discriminated from 1 (dark) to 4 (pale). As the infection progressed, the proportion of hepatopancreas score 1 decreased dramatically, while that of score 3 and 4 gradually increased. After the peak of mortality, the proportion of the surviving shrimp with hepatopancreas score 1 increased gradually, while the shrimp with score 3 and 4 decreased at recovery stage. In addition, we determined the V. parahaemolyticus load in the hepatopancreas and found that the higher the hepatopancreas score was, the higher the V. parahaemolyticus load. These data suggest that hepatopancreas color could be used to analyse the pathogenesis process of V. parahaemolyticus. And these results could help us to evaluate the shrimp resistance to Vibrio and further accelerate the breeding of disease resistant shrimp.