Abstract. Natural material of terrestrial plants is one of the environmentally friendly alternatives in preventing Vibrio alginolyticus. This study was aimed to know the effect of crude extract application of Alstonia acuminata shoot on the hematological change of sick humpback grouper Cromileptes altivelis. Hematology is an indicator effectively and sensitively used to monitor the physiological and pathological changes in fish. A. acuminata is a traditional terrestrial plant from eastern Mallucas, Indonesia, used to cure hepatitis, diarrhea, and malaria. This fact indicates that this plant contains chemical compounds as anti-bacterial and immuno-stimulant being able to control diseases, particularly in fish. Based on the post hoc test, there was significant difference between treatments for erythrocytes, leukocytes, and neutrophils, but significant difference between treatments for lymphocytes. The concentration of 200 ppm was the best concentration capable of curing the infected fish.

Key Words: blood, fish, disease, plant, Mallucas.