DIFFERENTIAL EXPRESSION OF IMMUNE RELATED GENES IN PACIFIC WHITE SHRIMP Litopenaeus vannamei PREVIOUSLY REARED IN BIOFLOC AND CHALLENGED WITH Vibrio harveyi

The biofloc has been developed to implement the use of minimum water exchange in aquaculture ponds .  It has been suggested  that biofloc  possess a probiotic effect and has a role on mechanisms related to the immune response in shrimp (Aguilera‐Rivera et al., 2018, 2014; Cardona et al., 2015; Ekasari et al., 2014; Ji et al., 2009; Kim et al., 2014). However, it is still unknown if there is a possible decrease in disease tolerance in shrimp reared in biofloc during an infection challenge. The aim of this study was to evaluate the possible up‐ or  downregulation of some genes related to the immune response in juveniles of L.  vannamei previously reared in biofloc and then challenged with different  densities of a pathogenic strain of V . harveyi.

Juvenile  L. vannamei  (15.88 ± 1.93 g) previously reared in biofloc were acclimated  and used for the bacterial challenge (Aguilera-Rivera et al. , 2018 ; Wang et al., 2014 ).  100 µL of the  V. harveyi CAIM1792 strain (Soto-Rodríguez et al., 2012) was prepared at different bacterial densities (from 10³ to 10⁸ CFU mL^-1) and used for the bacterial challenge, having 6 treatments and a control group (without bacteria ). After 10 days, a portion of muscle for every shrimp was taken and preserved in a stabilizing solution at -80°C for amplify the a2M, proFO , Hc and pen3a genes with q-PCR (Aguilera-Rivera et al., 2018). Relative gene expression data were analyzed using multivariate analyses. The contribution of genes on different bacterial densities were identified by PCA analysis, supporting the tendency obtained by plot means of every gene analyzed.

The data presented here suggest that with increasing  V. harveyi density, the tolerance threshold for the biofloc rearing system of  shrimp can be inefficient, and disease and mortality are observed regardless  of the fact that the immune response mechanisms in shrimp that prevent this negative effect are overstimulated.