en fish disease fish disease پژوهشي Orginal research papers The potential of milky mangrove <em>Excoecaria agallocha</em> leaf extracts has been utilized in traditional medicine in various parts of the world. Blood is an important indicator of health and is a pathological mirror of the entire body. Therefore, the effects of <em>E. agallocha</em> leaf extract on hematology indices of hybrid tilapia (<em>Oreochromis niloticus</em>) were investigated. Experimental fish were randomly divided into seven groups. Groups 1 to 5 were fed medicated feed at five different concentrations (10, 20, 30, 40 and 50 mg kg^-1) of <em>E. agallocha</em> leaf extract. Group 6 was given Flumequine (25 mg kg^-1) and group 7 was fed with untreated feed (control) for 28 days before they were intraperitoneally exposed to 4x10⁵cfu CFU ml^-1 <em>S. agalactiae</em>. The results revealed that the group fed medicated feed at 50 mg kg^-1 was the most effective concentration and showed no significant difference (<em>p</em>>0.05) compared to control and antibiotic groups on blood parameters (red blood cell, globulin, total serum protein, mean cell hemoglobin, and mean cell hemoglobin concentration) with the highest survival rate 99.67% within experimental groups. Overall, our results indicated the potential of <em>E. agallocha</em> could prove to be a hematological profile enhancer which can help fish combat bacterial infections. It was concluded that increase in the white blood cell count observed in fish administered with <em>E. agallocha</em> leaf extract at 50 mg kg^-1 suggests that <em>E. agallocha</em> extract contains agents that could stimulate the production of leucocytes and serve as an immune booster and prevent the risk of anemia. Streptococcus agalactia, Hematology, Hybrid tilapia, Excoecaria agallocha, Survival. 2512 2531 http://jifro.ir/browse.php?a_code=A-10-2146-1&slc_lang=en&sid=1 A.A. Laith saiflaith3@yahoo.ca 100319475328460036419 100319475328460036419 Yes School of Fisheries and Aquaculture Sciences, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu Malaysia M.A. Ambak mag@umt.edu.my 100319475328460036420 100319475328460036420 No nstitute of Tropical Aquaculture (Akuatrop), Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu Malaysia A. Jabar a.jabar90@gmail.com 100319475328460036421 100319475328460036421 No Zhejiang University, School of Medicine, Hangzhou, China, 31005 M. Najiah najiah@umt.edu.my 100319475328460036422 100319475328460036422 No School of Fisheries and Aquaculture Sciences, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu Malaysia