Peripheral blood and head kidney haematopoietic tissue response to experimental blood loss in mullet (Mugil cephalus)

Changes in haematological parameters and differential leukocyte counts of peripheral blood and head kidney haematopoietic tissue of mullet were assessed after an experimental anaemia, induced by caudal blood extraction. Thirty fish were used and divided into two groups: Group A (control group n = 20) and Group B (experimental group n = 10). From Group A, 10 fish were sacrificed to obtain head kidney control; from the 10 remaining, blood samples were collected by caudal venipuncture. From Group B, blood samples were collected five times once a week (T0, T1, T2, T3, T4) to induce experimental blood loss. At the end of the experimental period fish were sacrificed and the head kidneys were isolated. For all fish, haemogram and manual differential leukocyte counts were determined in peripheral blood. Reduced red blood cell count (RBC), haematocrit (Hct), haemoglobin (Hb), thrombocyte count (TC), lymphocytes and increased mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), monocytes and neutrophil values were found at T1 with respect to T0. Successively, until T3, RBC, Hct, Hb, TC and lymphocyte values showed an increase in peripheral blood. A decrease of haematological parameters in peripheral blood after the last bleeding time (T4) was observed. Cell identification and differential counts on head kidneys were performed and a significant increase of lymphocytes, monocytes and early unidentified blast cells was observed. A decrease in RBC, neutrophils, eosinophils, TC and a total absence of basophils were found. These results indicated that mullet are able to recover from anaemia caused by various adverse environmental and/or nutritional factors.