Abstract: Total superoxide dismutase（T-SOD）activities were investigated in hepatopancreas, muscle and gill of Macrobrachium nipponense at 3 h, 6 h, 9 h, 12 h, 24 h, 5 d and 10 d after being challenged by Streptococcus dysgalactiae equisimilis at levels of 0.6×10⁶, 2×10⁶, 4×10⁶ or 6×10⁶ CFU/mL in this study. Results showed that activity of T-SOD in hepatopancreas of the prawn reached the maximum at 5 d after infection. The values in muscle and gill reached to a maximum at 6 h. The activities of T-SOD in the hepatopancreas and gill of prawns infected with 6×10⁶ CFU/mL bacteria, in the muscle of prawns infected with 4 × 10⁶ or 6 × 10⁶ CFU/mL bacteria at 10 d decreased to about half of that in the control group. And the maximum in muscles was higher than those in hepatopancreas and gills. The results showed that Streptococcus dysgalactiae equisimilis could affect the activity of SOD in M. nipponense, and the response of the prawn to the bacteria was different in hepatopancreas, muscle and gill.

Key words: Streptococcus dysgalactiae equisimilis, Macrobrachium nipponense, total superoxide dismutase（T-SOD）