Histopathology of kidneys, spleens and intestines of C. auratus after immunization and bacteria challenge (H & E×400 magnification). A, B and C represent the sections of the kidneys, spleens and intestines, respectively. C. auratus were passive immunization NC (blank serum) and challenged with A. hydrophila (a) and P. fluorescens (c). C. auratus were passive immunization Slp mouse serum and challenged with A. hydrophila (b) and P. fluorescens (d). After bacteria challenge, glomerular atrophy, nuclear apoptosis and incomplete organisational structure were observed (Aa and Ac); less nuclear density and loose organisational structure (Ba and Bc); and abscission of intestinal villous epithelial cells, myometrial cells apoptosis, and degeneration were observed (Ca and Cc). Thus, passive immunization with Slp mouse serum can reduce the injury to the kidney, spleen and intestine.