The Effect Of Ghrelin On The Resistance Of Hybrid Tilapia To Aeromonas Hydrophila Infection

Aeromonas hydrophila is a common pathogenic bacterium.Previous studies in tilapia mainly focus on the treatment of A.hydrophila infection by Chinese herbal medicine and antibiotics,while the research on the anti A.hydrophila infection by fish autoimmune disease resistance factor is insufficient.Ghrelin is a polypeptide hormone secreted by gastrointestinal tract,which has many physiological functions such as regulating appetite,metabolism,growth and gonadal development of fish.Recent studies have shown that ghrelin can regulate the immune system.The aim of this study was to investigate the effect of ghrelin on the infection of hybrid tilapia(Oreochromis niloticus×O.aureus)by A.hydrophila.The main research contents and results are as follows:1.Sequence analysis and expression and of ghrelin in hybrid tilapia.RT-PCR and q PCR were used to analysis the sequence and expression of ghrelin gene.The coding region of ghrelin in hybrid tilapia is 324 bp,which encoded 107 amino acids.The Ghrelin m RNA expression was mainly expressed in the hybrid tilapia.The expression of Ghrelin was significant higher in the hybrid tilapia and Nile tilapia compared to Blue tilapia.2.The chemical synthesis of ghrelin,the control effect of ghrelin on A.hydrophila infection of hybrid tilapia and the bacteriostatic effect of ghrelin on A.hydrophila.Juvenile hybrid tilapia fish(20.28±1.03 g)were intraperitoneally injected with 0,0.1,1.0,or 10.0 ng/g synthetic ghrelin and A.hydrophila(0.5×10~6 cfu).After 10 days of injection,the survival rate of the control group was the highest.The survival rate of the 1.0 ng/g group(66.66%)was higher than that of the A.hydrophila group(13.33%).Therefore,ghrelin peptide injection can improve the survival rate of tilapia after infection and effectively protect tilapia.The bacteriostatic circle of A.hydrophila culture was tested by ghrelin,the results showed that ghrelin had no significant inhibitory effect on the growth of A.hydrophila.3.Ghrelin was used to analyze the histopathology,serum physiological and biochemical indexes,immune factor related indexes of hybrid tilapia infected by A.hydrophila.Histological analysis showed that ghrelin injection could reduce the pathological changes of liver and spleen caused by A.hydrophila infection in hybrid tilapia.Compared with the control group,there was no change of immune or antioxidant related indexes in the serum of tilapia injected with A.hydrophila.In general,the expression of HSP70,IL-1βand TGF-βin the liver was up-regulated compared with the control group.The levels of HSP70,IL-1βand TGF-βin renal tissue were up-regulated and TNF-αexpression was down regulated.The expression of IL-1β,TGF-βand TNF-αin spleen of hybrid tilapia was significantly increased.In conclusion,the expression of ghrelin gene sequence in the tissues of hybrid tilapia was concentrated in the stomach.Ghrelin may enhance the ability of hybrid tilapia to resist A.hydrophila infection by improve the self-immune ability.In this study,ghrelin can effectively improve the immune response ability of hybrid tilapia,and provide a new direction and data accumulation for the prevention and treatment of fish diseases.