Zebrafish larvae (5 dpf) were infected with 200 T. carassii or injected with PVP as non-infected control. Images are selected frames depicting the caudal artery, extracted from high-speed videos where trypanosomes (white open-arrow heads) and red blood cells (RBC, black open-arrow heads) were identified and tracked. (A) Artery of a control, non-infected, fish. Only RBC are present. (B) Artery of an infected fish, 1 dpi, showing a high ratio of RBC:trypanosomes. This frame corresponds to seconds 04:20-04:23 in Video 3, where the same trypanosomes were tracked. (C) Artery of an infected fish, 6 dpi, showing a reduced ratio of RBC:trypanosomes, indicating the onset of anaemia. (D) Artery of an infected fish suffering from severe anaemia, 8dpi, where only trypanosomes are present. The frame is extracted from the corresponding Video 9. Scale bars indicate 25 µm.