Iron loss and hypoxia are involved in lethal Pseudomonas plecoglossicida infections in the orange-spotted grouper Epinephelus coioides

Pseudomonas plecoglossicida is a causative agent of disease in aquaculture, leading to massive mortality in a variety of economically important cultured fish and resulting in great economic losses. Here we revealed that P. plecoglossicida infection caused a 62% probability of visceral white spot disease in orange-spotted grouper (Epinephelus coioides). After P. plecoglossicida challenge, the spleen mass increased significantly and the liver mass decreased significantly. Spleens had the highest bacterial load, at 1.38 x 107 colony forming units per gram. In addition, the number of blood red blood cells decreased. Moreover, diseased fish suffered from anemia and hypoxia. In addition, ferritin in the spleen was reduced, and there was a loss of iron in the fish. Furthermore, histological examination of the spleen showed that abundant red blood cells had infiltrated and that collagen fibers had been dissolved. In contrast, the survivors' spleens were rich in ferritin, having few red blood cell infiltration and collagen fibers that were intact. In summary, spleen collagen fibrinolysis, red blood cell infil-tration, and ferritin loss were demonstrated to cause hypoxia in the fish, which may be the reasons of death caused by P. plecoglossicida in orange-spotted grouper.