| Yellow catfish（Pelteobagrus fulidraco）is an important economically farmed fish in China,with an annual production of 500,000 tons according to China Aquaculture Network,and is the most common intensively farmed fish.In recent years,the aquaculture industry has been developing rapidly with the promotion of intensive culture mode,but factors such as high-density feeding and improper management often cause the deterioration of the water environment and affect the health status of aquatic economic animals.The fish intestine is a tubular digestive organ in the fish,and its health is closely related to its growth,nutrient digestion and absorption,and health status,and is also an important barrier against the invasion of intestinal pathogens and harmful substances.so the changes and mutual combinations of intestinal closure proteins are particularly important.Therefore,during the breeding process,yellow catfish often leads to the symptoms of intestinal pathology due to intensive breeding,which affects the yield.So the threat of lipopolysaccharide and ammonia is often faced in intensive culture.Lipopolysaccharide serves as a common immune system stimulant for many fish species,while ammonia is the most common water toxicity in culture.The search for ways to alleviate intestinal inflammation caused by lipopolysaccharides and ammonia has become a primary goal.In the process of research,it was found that vitamin D3 is a fat-soluble vitamin,which is involved in a variety of physiological functions in the body,but vitamin D3 must be taken from food to maintain the normal metabolism of the body,and there has been experimental evidence that vitamin D3has certain positive effects on the intestine.So whether vitamin D3 can alleviate the intestinal inflammation caused by lipopolysaccharide and ammonia stress in yellow catfish becomes an important target.In this study,we investigated the effects of lipopolysaccharide and ammonia stress on intestinal health indicators and enteritis in yellow catfish as experimental objects.As well as whether vitamin D3 can alleviate the occurrence of intestinal damage and enteritis caused by lipopolysaccharide and ammonia stress,it provides basic information for the coping strategy at the early stage of environmental impact outbreak,which is important for the healthy and sustainable development of aquaculture industry.1.Effect of lipopolysaccharide-induced acute enteritis in yellow catfish on occluded protein and the mitigating effect of vitamin D3In this experiment,a 96 h acute lipopolysaccharide stress experiment was conducted on yellow catfish,divided into four groups:control group（saline injection）,lipopolysaccharide group(4 mg/kg-1),vitamin D3 group(6.5 IU·kg-1)and lipopolysaccharide plus vitamin D3 group,with 120 fish in each group.The results showed that the expression levels of intestinal antioxidant enzymes（superoxide dismutase and catalase）in yellow catfish showed a trend of decreasing（24 h）and then increasing under lipopolysaccharide stress.The expression of intestinal inflammatory genes（interleukin 1β,8 and tumor necrosis factorα）and apoptosis-related genes（Caspase-3,Caspase-9 and Bax）was consistently increasing.The expression levels of tight junction proteins in the intestinal barrier showed a trend of increasing after being suppressed at the beginning（24 h）.Compared with the control group,antioxidant enzyme activity was inhibited and inflammatory factors were upregulated in the lipopolysaccharide group,and barrier-type Claudin protein expression was inhibited and channel-type protein expression was increased in the intestine,indicating that lipopolysaccharide stress led to disruption of intestinal structure and function.In the vitamin D3 group,the activity of antioxidant enzymes was increased,the expression of inflammatory factors was decreased and the expression of barrier-type proteins was up-regulated,indicating that vitamin D3 has a positive effect on intestinal health.Compared with the lipopolysaccharide group,in the lipopolysaccharide plus vitamin D3 group,the addition of vitamin D3 enhanced the activity of antioxidant enzymes,decreased the expression of pro-inflammatory factors and enhanced the expression of anti-inflammatory factors,and effectively enhanced the expression of barrier-type proteins and decreased the abnormal expression of channel-type proteins,indicating that the addition of vitamin D3 could alleviate the adverse changes in the intestinal tract of yellow catfish under lipopolysaccharide stress and play a protective effect on the organism.The results showed that a series of adverse reactions occurred in the intestine of yellow catfish under lipopolysaccharide stress,and the addition of exogenous vitamin D3 largely alleviated the adverse effects and improved the health status of the organism.2.Effect of ammonia-induced acute enteritis in yellow catfish on occluded protein and the alleviating effect of vitamin D3In this experiment,a 96 h ammonia stress experiment was conducted on yellow catfish.It was divided into control group（saline injection）,ammonia group（57 mg/L）,vitamin D3group(6.5 IU·kg-1)and ammonia nitrogen plus vitamin D3 group with 120 fish in each group.The results showed that the expression levels of intestinal antioxidant enzymes（superoxide dismutase,catalase,glutathione peroxidase and glutathione reductase）of yellow catfish increased in the first period（24 h）and then decreased slowly under ammonia-stress.The expression levels of intestinal inflammatory genes（interleukin 1β,8,10 and tumor necrosis factorα）also increased at 24 h and then decreased,while the expression of apoptosis-related genes（Caspase-3,Caspase-9 and Bax）was continuously increasing and the expression levels of tight junction proteins in the intestinal barrier were first inhibited and then increased.In contrast,the addition of vitamin D3 caused benign changes in the intestine:an increase in antioxidant enzyme activity,expression of apoptotic genes,expression of pro-inflammatory factors,expression of tight junction proteins,and serum immune protein levels in the ammonia group compared with the control group,along with an inhibition of expression of anti-inflammatory factors,indicated that ammonia stress had adverse effects on the intestine.In the vitamin D3 group,the activity of antioxidant enzymes and the expression of anti-inflammatory factors were elevated and the serum immunoprotein content was reduced,indicating that vitamin D3 acts as an immune enhancer.Compared with the ammonia group,in the mixed group of ammonia and vitamin D3,the activity of intestinal antioxidant enzymes was reduced and returned to normal,the expression of pro-inflammatory factors was inhibited and simultaneously promoted the expression of anti-inflammatory factors,the expression of apoptotic genes was inhibited,and the expression of tight junction proteins was reduced and converged to normal while reducing the content of serum immunoproteins,indicating that vitamin D3 played a protective and The results indicated that vitamin D3 played a protective and immune enhancing role in ammonia stress.The results showed that a series of adverse reactions and immune responses occurred in ammonia stress in yellow catfish,and the addition of vitamin D3 alleviated this situation and played a role in immune enhancement,which reduced the damage in ammonia stress in yellow catfish.In conclusion,whether it is lipopolysaccharide or ammonia stress,the intestinal tract of yellow catfish will be irreversibly damaged,which will lead to lesions of the organism and serious death.The addition of vitamin D3 will reduce the damage and enhance the anti-stress ability of the organism,so as to reduce the lesions and even death of yellow catfish due to intestinal inflammation during the breeding process.In the future,this can be used as a basis to further develop the linkage between closely linked proteins and other aspects of the aquaculture process,and to create new species that are healthier and have stronger resistance to stress,as well as to provide a theoretical basis for disease control in aquaculture. |
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