| Tilapia is an important breed of freshwater aquaculture in China,mainly in Guangdong,Hainan,Guangxi,Yunnan and Fujian provinces.In recent years,the promotion of large-scale aquaculture model and deterioration of aquaculture environment lead to frequent diseases,of which streptococcus disease is the most harmful.There are no reports of the way of tilapia-infected Streptococcus agalactiae infestation and target organ.The study of dynamic pathology and immunological enzyme activity of tilapia-infected Streptococcus agalactiae can provide a theoretical basis for further study on the pathogenesis of Streptococcus agalactiae and the development of drug-control drugs.In this study.Gibberella multiflorus was infected with Streptococcus agalactiae(HN016 strain)by injection,intragastric administration and soaking.The distribution and pathological changes of pathogens in group tilapia were observed and studied.At the same time,the study will focus on changes of immune-related enzymes in blood and liver tissues of different populations of tilapia after infection with Streptococcus agalactiae.The main conclusions are as follows:(1)Infection of GIFT was carried out by injection,gavage and soaking.The clinical symptoms of typical Streptococcus agalactiae were observed in the injection and gavage.The death period of the injection group was the shortest and dead fish were found 12 hours later after infection.The death rate was the highest at 24 hours later after infection and the mortality rate was highest,up to 92.5%.The dead fish in gavage group were found 5 hours later after infection.The highest mortality rate was 48 hours later after infection,and the death rate was 90%after infection.Fish in soaking group had only mild symptoms,and no dead fish.(2)After GIFT infected Streptococcus,pathogens in their body were isolated.The spleen,liver,anterior kidney,stomach,cheek,skin and muscle tissue of the fish in the injection group and gavage group can be isolated pathogens after 2 hours of infection,the brain tissue can be isolated pathogens 5 hours after infection in the two groups.The significant symptoms in the two groups were shown 8 hours after infection.At this time,the pathogen of the body tissue concentration reached the peak;while,the pathogen in soaking group were isolated from of the body tissues 8 hours later after infection,but their concentrations were lower than those of the other two group at the same time.(3)After GIFT were infected Streptococcus in the way of injection,gavage and soaking,the infested gill,intestine,spleen and liver tissue of fish were handled by hematoxylin-eosin staining(HE staining)and immunohistochemical localization.HE staining showed that there were obvious lesions in the gills,liver,spleen and intestine at the early stage(2-5 hours)after infection.The gill showed the proliferation of the epithelial cells and the necrosis of the gills.The macrophages diffuse infiltration and the blood vessels become thinner,the liver for the vacuolar degeneration,capillary rupture,intestinal villi rupture,submucosal cell structure was destroyed;The degree of disease of three ways were followed by injection group>gavage group>soaking group.The results of immunohistochemical staining showed that the strong positive signal of the pathogen was in the intestinal tissue in gavage group,the spleen tissue in injection group,and the gut tissue in soaking group.(4)Streptococcus agalactiae(HN016 strain)were infected with GIFT,Nile tilapia and Oreochromis niloticus,by intraperitoneal injection.We analyzed the change of SOD,ACP,AKP,LZM and T-AOC in the blood and liver of three kinds of tilapia.The results showed that the activities of ACP,AKP,LZM,SOD and T-AOC in three different tilapias presented increased first and then decreased,while CAT activity presented decreased first and then increased.And 24 hour later CAT,ACP,AKP,LZM activity in three kinds of tilapia blood showed a rising trend. |
PDF Full Text Request