Banjarnegara is one of the North African catfish (Clarias gariepinus “Burchell 1822") cultivation centers in Central Java Province, Indonesia. However, problems are often found in the field, one of which is aeromoniasis caused by Aeromonas hydrophila. Extract of Avicennia marina can be used as an alternative natural treatment. The study aimed to conduct a field-testing using a methanol extract of A. marina to treat the infected North African catfish by A. hydrophila in the Banjarnegara region, Indonesia. The research method was experimental using a completely randomized design with 4 treatments and 4 replications, namely P0: not treated with the extract (control), P1: 0.2 g L^–1, P2: 0.3 g L^–1, and P3: 0.4 g L^–1. This study showed that the clinical signs in the North African catfish after infection with A. hydrophila were ulcers, lesions, depigmentation, abdominal dropsy, hyperemia, hemorrhagic, and exophthalmia. The recovery process appeared in P1, P2, and P3 on days 4-5, except for the control group. In addition, P1, P2, and P3 treatments could increase the survival rate (P< 0.05) to 74.95-84.95%, compared to the control group (P0), which was 6.6%. Meanwhile, the increase in the weight and length of the fish in all treatments were not significantly different (P˃ 0.05). In conclusion, the leaf methanol extract of A. marina is effective and efficient in treating A. hydrophila infection for the North African catfish at 0.2g L^–1.