The regulation mechanism of hematopoiesis during ischemic and hemolytic anemia in grass carp(Ctenopharyngodon idella)

Grass carp (C. idella) is an important farmed freshwater fish in China. In recent years, grass carp hemorrhagic diseases caused by viruses, bacteria, and parasites have hindered the aquaculture industry; however, there are few studies on the hematopoiesis of grass carp. It is reported that erythropoiesis is a complex biological process, which requires hematopoietic-stimulating factors, inhibitors, the hematopoietic microenvironment, and stromal cells to interact for fine regulation. In this study, ischemic anemia (a blood loss model) and hemolytic anemia (a hemolysis model) were established to stimulate hematopoiesis of grass carp. The hematopoietic organs of grass carp were studied using tissue imprinting, hematoxylin-eosin (H&E) staining, western blot (WB), and immunofluorescence assay (IFA). Hematopoietic-stimulating factors and iron metabolism-related factors were detected by quantitative real-time PCR (qRT-PCR). The results of tissue imprinting showed that there were proerythrocytes in the head kidney, spleen, and middle kidney. In the model of ischemic anemia, a hematopoietic island could be found in head kidney and spleen at 24 h. The hematopoietic island appeared in the middle kidney on the 7th day. The results of H&E staining showed that when the peripheral blood decreased sharply, the spleen compensated for the peripheral blood and decreased the melanin macrophage center in head kidney, spleen, and middle kidney. The results of WB, IFA, and qRT-PCR showed that the hematopoietic pathway and iron metabolism were activated in both models. In sum, the head kidney, spleen, and middle kidney of grass carp are its main hematopoietic organs, and the head kidney is the most important. The spleen is an important blood bank of grass carp and hematopoiesis compensation occurs in the spleen and mesonephros during severe ischemia.