ETosis in tambaqui Colossoma macropomum: A programmed cell death pathway and approach of leukocytes immune response

Tambaqui Colossoma macropomum is the most cultivated native fish in South America and Aeromonas hydrophila is one of the main bacteria infecting tropical fish. Despite the economic importance of this round fish, to date, there has been a paucity of investigations into haematological changes in tambaqui. In this study, detailed blood analyses (0 h, 6 h, 24 h, 7 d and 14 d) following intraperitoneal challenge with A. hydrophila were performed. After analysing the results, there was a suspicion of a novel cell death mechanism via extracellular traps (ETosis) in tambaqui. The search for ETosis was based on differential interference contrast (DIC) microscopy and scanning electron microscopy (SEM) assays through application of an adapted protocol applying co-incubation of leukocytes with A. hydrophila. The cells were investigated at: 0 h (control), 4 h and 7 h after incubation. The complete haemogram profile showed an uncommon severe leukopenia in early phases of infection (6 h, p