Differential expression of immune‐related genes in Pacific white shrimp, Litopenaeus vannamei, previously reared in biofloc and challenged with Vibrio harveyi

Abstract

This study aimed to evaluate possible modification of some immune-related genes (hemocyanin, alpha2-macroglobulin, prophenoloxidase and penaeidin3a) at the transcriptional level and signs of disease and mortality in Litopenaeus vannamei previously reared in biofloc and challenged with different Vibrio harveyi densities (103–108 CFU per ml). Gene expression was up- or downregulated based on bacterial density, indicating that defence mechanisms were activated to remove the pathogen. The genes analysed were not affected in the control group (without bacteria) or in the 103 CFU per ml group. The prophenoloxidase gene was expressed in the 104 CFU per ml group, whereas transcripts of the alpha2-macroglobulin gene were detected in the 105 and 106 CFU per ml groups. However, the penaeidin3a and hemocyanin genes were upregulated in the 107 and 108 CFU per ml groups, in which signs of disease and mortality in shrimp were evident. These results suggest that the genes involved in the shrimp immune response fluctuate according to pathogen density, and when this density increases (e.g. 107 and 108 CFU per ml), the activated disease tolerance and defence mechanisms are inefficient. For this reason, disease and mortality were observed in the shrimp regardless of the previous condition of the biofloc.