| Summary: | Ammonia-N is toxic to many aquatic animals and serves as a key stress factor in aquatic environments. The effects of ammonia-N stress on the immune response of darkbarbel catfish Pelteobagrus vachellii were investigated in this study. Changes in overall histology, and in the expression of complement C3 and immunoglobulin M (IgM) in spleen and head kidney, and lysozyme and C3 in serum, were measured in 1 and 5 mg/L ammonia-N. Hyperemia, melano-macrophage assembly and loose splenosis were evident in spleen tissue. Both lysozyme and component C3 were significantly reduced in serum (P < 0.05) under both stress treatments, although lysozyme was increased slightly at 24 h in the 1 mg/L treatment. C3 mRNA expression increased at 6 h in spleen and 6–12 h in head kidney then decreased rapidly (P < 0.05), although C3 mRNA recovered to control levels in spleen at 96 h after the 1 mg/L treatment (P > 0.05). IgM expression also increased significantly at 6–12 h in spleen and 6–24 h in head kidney after the 1 mg/L treatment (P < 0.05). A similar overall pattern were observed with 5 mg/L ammonia (P < 0.05); IgM mRNA expression was elevated at 6 h in spleen and 6–12 h in head kidney (P < 0.05) then decreased to levels below controls (P < 0.05). These results suggest exposure to 5 mg/L ammonia-N could damage the histological structure of spleen, diminish lysozyme and component C3 serum content, and suppress C3 and IgM expression in spleen and head kidney.
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