Histopathological Observation of Aeromonas hydrophila Infection and Influences on Immune-related Enzyme Activity Indexes in Carassius auratus indigentiaus subsp. Nov.

Abstract

Bacterial sepsis caused by Aeromonas hydrophila infection is one of the most common infectious diseases of Carassius auratus indigentiaus subsp. Nov. It has characteristics of quick onset, high morbidity, and high mortality. Bacterial sepsis has become an important constraint against the industrialization of aquaculture of Carassius auratus indigentiaus subsp. Nov. In this study, Carassius auratus indigentiaus subsp. Nov. were immersed in 1.0×109 CFU/mL Aeromonas hydrophila for infection, the cumulative mortality at 1d, 3d, 5d, 7d and 14d were 10%, 26.67%, 40%, 40% and 40%, respectively. After being challenged with Aeromonas hydrophila, hemorrhage focus and suppuration were observed on the body surface, pelvic fin, anal fin, and tail fin base of Carassius auratus indigentiaus subsp. Nov. Dissecting Carassius auratus indigentiaus subsp. Nov., blackening of the spleen and hemorrhage at the liver were discovered at 3d after being infected with Aeromonas hydrophila. Through tissue section observation, liver tissue was found to have to hemorrhage focus, and vacuolated liver cells, accompanied by inflammatory cell penetration. Inflammatory cell infiltration was also observed in spleen tissues and was most serious at 3d day after infection. After being infected with Aeromonas hydrophila, the gill filaments of Carassius auratus indigentiaus subsp. Nov. were deformed and shortened, gill filament cells fell off, intestinal villi are shortened and mucus cells are increased. After Aeromonas hydrophila infection to Carassius auratus indigentiaus subsp. Nov., the lysozyme content and activities of catalase, alkaline phosphatase, and total superoxide dismutase (T-SOD) in the liver began to increase significantly after the first day and reached a peak on the third day. However, they began to decrease gradually on the fifth day. The acid phosphatase (ACP) activity increased dramatically after the first day, peaked on the fifth day, and then decreased on the seventh day. It is speculated that such changes were attributed to the following two aspects: 1) On the one hand, Aeromonas hydrophila infection stimulates the nonspecific immune system of Carassius auratus indigentiaus subsp. Nov. 2) On the other hand, lesion of tissues occurs after Aeromonas hydrophila infection of Carassius auratus indigentiaus subsp. Nov. reaches a certain extent, thus influencing lysozyme content and the catalase activities, ACP, alkaline phosphatase and T-SOD in the liver.