Abstract: In order to explore the response of apoptosis related genes in the spleen of Trachinotus ovatus infected by Streptococcus agalactiae, we infected the spleen tissues of T. ovatus by S. agalactiae for a pathological observation. The blood routine indexes of the fish before and after infection, as well as different times (0 h, 6 h,12 h, 24 h, 48 h, 72 h, 96 h, 120 h) after infection, the serum lactate dehydrogenase (LDH), spleen alkaline phosphatase (ALP), and acid phosphatase (ACP) and quantitative analysis of Caspase-3, Caspase-8, and Caspase-9 genes. The results reveal that after artificial infection with S. agalactiae, the body of T. ovatus showed obvious pathological changes, mainly manifested as protruding eyes, turbidity and bleeding. Histopathological observation shows that the spleen tissue had inflammatory lesions. Compared with the control group, the number of red blood cells (RBC), hemoglobin concentration (Hgb) and hematocrit (HCT) in the infected group decreased significantly, while the number of white blood cells (WBC), neutrophils (NE) and lymphocytes (LYM) increased, and the mean red blood cell volume (MCV) increased. The activities of serum LDH, spleen ALP and ACP were up-regulated with time. The expressions of Caspase-3, Caspase-8 and Caspase-9 were significantly up-regulated in spleen. The results show that the body of T. ovatus infected by S. agalactiae had an obvious immune response.