Immune response of selective breeding striped catfish families (Pangasiandon hypophthalmus) to Edwardsiella ictaluri after challenge

The present study attempted to understand the immune responses of resistant (RF) and susceptible families (SF) striped catfish (Pangasianodon hypophthalmus) of generation one tested and selected for resistance to Edwardsiella ictaluri, causative agent of bacillary necrosis of Pangasius. Two family groups including resistant (RF) and susceptible families (SF) with 30 individuals in each family were challenged with E. ictaluri. There were three families in each study group. After challenge, totally 1547 samples of the blood, serum, kidney, liver and spleen were collected at five different time points including prior infection, 24, 48, 264 and 312 h post infection (hpi) to assess immune responses of the fish. Data were tested for probability of normal distribution by Skew and Kurtosis tests. Results showed that the non-specific immune response of the RF group was more effective than that of the SF group. The red blood cells in RF group were destroyed slowly while the white blood cells in RF group increased significantly starting from 48 hpi as compared with those of the SF group. In contrast, the white blood cells in SF group displayed a significantly slower increase, mainly after 264 hpi. In addition, the development of monocyte and neutrophil of the RF families was faster than that of the SF and the number of melano-macrophage center of the RF was also higher than that of the SF at 24-48 hpi. Finally, the specific immune response (antibody titer) of the RF group was higher than that of the SF group. Our study showed that 24-48 hpi was the most critical period to differentiate the disease resistant individuals with the Area Under the Curve (AUC) value of the model for identifying resistant individuals of 0.95.