| Sebastes schlegelii is one of the main fish species in the deep-sea cage culture in northern China and is a near shore cold-water carnivorous fish with the characteristics of low temperature resistance. With the further expansion of the breeding scale and the increase of the breeding density, the diseases found at this stage mainly include eye rot, bacterial enteritis, skin ulcer disease, etc. It is caused by a variety of bacteria, and Photobacterium damselae subsp. damselae, (PDD) is a gram-negative pathogen widely distributed in the global marine environment, which can infect a variety of marine animals such as Sebastes schlegelii, and the pathogenic cases in China""s marine aquaculture industry are gradually increasing and the pathogenic hosts are diversified, which poses a new threat to the healthy development of China""s marine aquaculture industry.
So in this paper, we focused on the deep-sea aquaculture of Sebastes schlegelii in the Huang Bohai, and studied the effects and mechanisms of Sebastes schlegelii on PDD from the levels of cells, tissues, enzyme activity, immunity by histopathological, cellular, physiological and immune responseSebastes A body weight of 65.02±3.52 g and length of 15-17 cm were taken as the research object, and the normal saline injection was used as the control group (C), and the 3 d, 5 d, and 7 d after PDD infection were used as the experimental groups (D3, D5, and D7), with 3 replicates in each group, and 30 fish in each replicate, and the breeding experiment was carried out for 1 week. The results showed that PDD infection caused structural lesions of the intestine, spleen and liver, resulting in inflammation and oxidative stresSebastes After infection, the inflammatory response occurred in the scorpion Sebastes schlegelii, and the number of white blood cells decreased significantly, which verified the occurrence of inflammatory response. The results showed that PDD significantly affected the antioxidant performance (SOD, CAT, MDA, PO, MPO), non-specific immune performance (LZM, ACP, AKP, SIgA) and growth indexes (α-AL, PAMY, LPS) of the liver. The SOD activity in the experimental group was significantly lower than that in the control group, and the lowest activity was 10.26±0.11 U/g in the D3 group (P<0.05). The MDA content in the D3 and D5 experimental groups was significantly higher than that in the control group (P<0.05). The CAT activity in the experimental group was significantly lower than that in the control group (P<0.05), and the maximum decrease in enzyme activity in the D3 group decreased from 112.90±1.56 U/g to 66.81±1.04 U/g. The activity of PO enzyme increased first and then decreased, and the activity was significantly higher than that of the control group (P<0.05) at three days, reaching 110.01±2.39 U/g. MPO showed a unimodal shape, which first increased and then decreased, and the highest in the D5 group was significantly different from that in the control group (P<0.05). The maximum LZM activity in D3 in the experimental group was 3.41±0.21 U/mL, which was significantly higher than that in the control group, and showed a unimodal shape (P<0.05). The ACP activity of the experimental group D5 group reached a maximum of 280.23±2.91 U/mL five days after infection, which was significantly different from that of the control group (P<0.05). At the time of infection five days after infection, the activity of AKP in the experimental group D5 group reached the lowest (42.37±1.53 U/mL), which was significantly different from that in the control group (P<0.05). The activity of the D5 group in the SIgA experimental group reached 47.18±0.93U/g at five days after infection, and there was no significant difference between the D7 group and the control group (P>0.05). The trends of α-AL and PAMY increased first and then decreased, and there was a significant difference between the control group on the fifth day after infection (D5) (P<0.05). The changes of LPS decreased first and then increased, and the highest D5 in the experimental group reached 137.48±3.13 U/g, which was significantly different from that in the control group (P<0.05), and the lowest D3 in the experimental group was 111.26±2.64 U/g. PDD injection significantly affected the intestinal pancreatic amylase activity, lipase activity and α-AL activity of Sebastes schlegelii (P<0.05), and the enzyme activity results showed that PDD significantly affected the antioxidant performance, non-specific immune performance and growth indexes of Sebastes schlegelii liver. In addition, the changes in the expression levels of 11 mRNA genes in the intestinal immune genes, tight junction protein genes and related inflammation-related signaling pathway genes in the experimental group were significantly down-regulated by qRT-PCR on the intestinal immune genes, tight junction protein genes (Claudin-3, CLND-15, and ZO-1) and related inflammation-related signaling pathway genes (IL-10, and IL-12b) in the experimental group (P<0.05). In the experimental group, the relative mRNA expressions of intestinal inflammatory cytokines IL-8, IL-15 and IL-1β were significantly up-regulated，and the relative mRNA expression of related inflammatory pathway genes (NF-?Bp65, NLRC3.2, and MyD88) were significantly down-regulated (P<0.05).
The results showed that PDD infection could reduce the growth performance and antioxidant performance of Sebastes schlegelii scorpion, damage the tissue structure of the intestine, liver and spleen, lead to tissue lesions, down-regulate the relative expression of intestinal tight junction protein and anti-inflammatory factor genes, and up-regulate the relative expression of inflammatory factor geneSebastes In conclusion, through the implementation of this project, it will provide a scientific basis for the health evaluation of Sebastes schlegelii in the deep-sea environment, and also provide a scientific basis for the development of corresponding impressive technologies. |
