Tolerance Of Hybrid Tilapia And Its Parents To Streptococcus Agalactiae

In recent years,tilapia farming has become a frequent disease,and streptococcus has become the primary pathogen of tilapia farming,with high morbidity and mortality.Therefore,it is imperative to screen out the excellent varieties with strong disease resistance and provide a good guarantee for the sustainable development of tilapia healthy breeding.In this paper,the following work was carried out on the difference in resistance to streptococci in Hybrid tilapia and its parents:(1)To identify a blue tilapia(Oreochromis aureus)that is more resistant to the infection of Streptococcus,agalactiae,"Xia’ao No.1" strain(AX for short)and Egypt strain(AE for short)were artificially infected by S.agalactiae.The cumulative mortality was recorded at different time points.Blood and tissue samples were collected at 0h,7h,24h,48h,72h,120h and 168h after infection.The resistance to streptococcal disease were evaluated from the aspects of serum biochemical parameters,spleen pro-inflammatory cytokine and liver HSP70 expression.The results showed that the cumulative mortality of AX strain tilapia was significantly lower than that of AE strain tilapia;AX strain tilapia serum globulin/total protein(A/G),superoxide dismutase(SOD),valley The levels of alanine aminotransferase(ALT)and glucose(GLU)did not change significantly at 7h after infection(P>0.05),and the serum cholesterol(TC)content increased significantly at 7h after infection(P<0.05);two strains Luo Fei The contents of serum alkaline phosphatase(AKP),aspartate aminotransferase(AST),lactate dehydrogenase(LDH)and lysozyme(LZM)were significantly increased at 7h after infection(P<0.05).Serum triglyceride(TG)And the intensity of respiratory burst decreased significantly at 7h after infection(P<0.05),serum globulin(GLO)levels were not significantly different at 24h after infection(P>0.05);after infection with S.agalactiae,the relevant immune genes The expression levels of IL-1 β,IL-6,TNF-α and HSP70 were significantly increased,but the expression level of AX strain tilapia was higher than that of AE strain tilapia.The result showed that the AX strain has strong anti-streptococcal disease ability.(2)To identify Oreochromis spp.that is the most resistant to the infection of Streptococcus agalactiae,hybrid tilapia NA1(O.niloticus ♀×O.aureus ♂),its parents blue tilapia(O.aureus)" Xia’ao No.1" strain(AX for short)and Nile tilapia Egypt strain(NE for short)were artificially infected by S.agalactiae.The cumulative mortality was recorded at different time points.Blood and tissue samples were collected at 0h,7h,24h,48h,72h,120h and 168h after infection.The resistance to streptococcal disease were evaluated from the aspects of serum biochemical parameters,spleen pro-inflammatory cytokine and liver HSP70 expression.The results showed that the mortality of hybrid tilapia NA1 was significantly lower than that of the two parents;the A/G,AST and LZM activities of NA1 tilapia did not change significantly at 7h after infection(P>0.05).Serum SOD and GLU were significantly increased at 7h after infection(P<0.05),and serum GLO was significantly increased after infection(P<0.05).Serum AKP and LDH were significant at 7h after infection in three tilapia.There was no significant difference in serum ALT after infection(P>0.05),and the serum TG and respiratory burst intensity were significantly decreased 7h after infection(P<0.05).After infection with Streptococcus agalactiae The expression levels of related immune genes IL-1 β,IL-6,TNF-α and HSP70 were significantly increased.The expression level of NA1 tilapia was the highest,and the expression levels of the two parents were not much different.The result showed that the resistance of NA 1 tilapia to streptococcus is better than that of its parents.(3)To identify hybrid tilapia(O.niloticus ♀×O.aureus ♂)that is more resistant to the infection of Streptococcus agalactiae,hybrid tilapia NA1(O.niloticus Egypt strain ♀ X O.aureus " Xia’ao No.1" strain ♂)and NA2(O.niloticus "Xianghu" strain ♀ ×O.aureus" Xia’ao No.1" strain ♂)were artificially infected by S.agalactiae.The cumulative mortality was recorded at different time points.Blood and tissue samples were collected at Oh,7h,24h,48h,72h,120h and 168h after infection.The resistance to streptococcal disease were evaluated from the aspects of serum biochemical parameters,spleen pro-inflammatory cytokine and liver HSP70 expression.The experimental results showed that there was no significant difference in the cumulative mortality of the two tilapia(P>0.05);the serum A/G and AST levels of the tilapia NA1 tilapia did not change significantly at 7 h after infection(P>0.05);The levels of GLO,AKP,SOD,GLU and LDH in the serum of the two species of Oreochromis were significantly increased at 7h after infection(P<0.05).There was no significant difference in serum ALT and LZM levels at 7h after infection(P<0.05),the serum TC,TG and respiratory burst intensity decreased significantly after infection(P<0.05);the expression levels of related immune genes IL-1 β,IL-6,TNF-α and HSP70 after infection with Streptococcus agalactiae Significantly increased,but the expression of hybrid tilapia NA1 was higher than that of hybrid tilapia NA2.The result showed that hybrid tilapia NA1 can better cope with streptococcal stimulation.