Fish trypanosomiasis is a common blood parasitic disease transmitted by aquatic invertebrates, such as leeches. This study
aims to shed light on the cytotoxicity of Trypanosoma sp. on erythrocytes and its impacts on the innate immune response
(serum lysozyme activity, nitric oxide production, phagocytic activity, serum total protein, and globulin) in wild African
catfish, Clarias gariepinus. One hundred catfish were examined using blood smears stained with Giemsa and confirmed with
PCR. The prevalence of infection was found to be 10% by microscope detection and 15% by PCR. The morphological identification
of Trypanosoma as Trypanosoma mukasai was determined. Additionally, this study included previously undescribed
features of Trypanosoma, such as the width of the anterior and posterior body, the length of the posterior pale region, and
the number of folds. Various alterations in erythrocytes were observed, totaling 54.57%. Nuclear abnormalities, including
fragmented nuclei, eccentric nuclei, and micronuclei, were also reported. Infected fish showed a reduction in serum total
protein and globulin levels, while nitric oxide production, lysozyme activity, and phagocytic activity exhibited a significant
increase compared to non-infected fish. We believe that our findings will contribute valuable data to the morphological and
molecular identification of Trypanosoma sp. in African catfish, as well as their cytotoxic impact.