Assessment of the immune responses of macrophages in selective breeding pangasius families (Pangasianodon hypophthalmus) resistant to enteric septicemia of catfish (ESC)

This study aimed to evaluate the non-specific immune responses of macrophages in two selective breeding pangasius family groups: high disease-resistant (A) and low disease-resistant (B) to Enteric Septicemia of Catfish (ESC) caused by Edwardsiella ictaluri. Fish were sampled at five different time points after infection with the bacteria E. ictaluri including before the infection process, 24hpi, 48hpi, 264hpi and 312hpi. There were 372 samples including 192 samples of fish in group A and 180 samples in group B. All of them were used to analyze the amount of melano-macrophage centers in the tissues of liver, kidney and spleen; phagocytosis activity (PA) and phagocytosis index (PI) of the anterior kidney macrophages. Results showed that (1) the number of melano-macrophages of group A fish was higher than that of group B at survey points during the challenge and the difference was significant at 48hpi; (2) PA and PI of group A were higher than that of group B in the period from 48 to 264hpi, specifically, the PI of group A was higher than that of group B, which was statistically significant at 48hpi. The results of this study showed that the differences in non-specific immune responses through melano-macrophages can improve the survival rate and life span of the high disease-resistant family compared to the low disease-resistant family after the challenge with Edwardsiella ictaluri.