The impact of Aeromonas salmonicida infection on innate immune parameters of Atlantic salmon (Salmo salar L).

Enzyme activities and gene expression of a number of innate immune parameters in the serum, mucus and skin of Atlantic salmon (Salmo salar) were investigated after challenge with a pathogenic strain of Aeromonas salmonicida (A. salmonicida). Fish were injected in the dorsal muscle with either 100 µl bacterium solution, about 3.05 × 10(7) CFU/ml A. salmonicida, or 100 µl 0.9% NaCl (as control group) and tissue samples were collected at days 0, 2, 4 and 6 post-injection. Lysozyme (LSZ) and alkaline phosphatase (AKP) activities in serum, mucus and skin, and LSZ and AKP mRNA expression in skin of the challenged fish were higher than those of the control at most of the experimental time, with significant differences at several time points (P < 0.05), indicating the involvement of LSZ and AKP in the innate immunity of Atlantic salmon to A. salmonicida. Superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in mucus and skin, along with the SOD, POD and CAT mRNA expression in skin significantly decreased at day 4 and 6, indicating the decreased antioxidant capacity of the challenged fish. Glutamate pyruvate transaminase (GPT) and glutamic oxalacetic transaminase (GOT) activities in serum, mucus and skin of the challenged group were all higher than those of the control after the injection, and at several time points significant differences were found between the two groups, suggesting organs of fish were impaired after the pathogen infection. The changes of the GPT and GOT activities could be used as potential biomarkers for the impairment of physiological functions caused by the pathogen infection. Identified biomarkers of the immune responses will contribute to the early-warning system of the disease. So this study will not only provide a theoretical basis for vaccine development, but also provide basic data for the establishment of early warning systems for diseases caused by A. salmonicida in Atlantic salmon rearing.