| Carassius auratus is one of the most common freshwater fishes in China,with the advantages of fast growth,strong disease resistance,wide appetite and strong environmental adaptability.However,with the rise of high-density intensive breeding mode,the water quality has deteriorated,the resistance of carassius auratus has decreased,which will lead to carassius auratus being easily infected with Aeromonas hydrophila and the outbreak of bacterial diseases has become severe.Probiotics can regulate water quality,improve immunity of aquatic animals,and will not produce drug resistance,can fundamentally prevent and treat various bacterial diseases in carassius auratus.However,when the concentration of pathogenic bacteria is high,the prevention and treatment effect of probiotics on bacterial diseases in carassius auratus will be greatly reduced.Slightly acidic electrolyzed water sterilizes quickly and efficiently,is harmless to human body and environment,and not easy to remain.However,high concentration will damage the tissues of carassius auratus,while low concentration will lead to poor sterilization effect and cannot completely control the diseases.Therefore,this study combines the advantages of probiotics and slightly acidic electrolyzed water to jointly treat bacterial diseases in carassius auratus to reduce the use of antibiotics and disinfectants.In order to find a green,efficient and safe prevention and treatment method for bacterial diseases in carassius auratus.The main research contents and results are divided into the following aspects:1.In order to study the bactericidal effect of slightly acidic electrolyzed water on Aeromonas hydrophila under different conditions.In this experiment,after treating Aeromonas hydrophila with slightly acidic electrolyzed water with available chlorine concentration of 30 mg/L,plate counting method,scanning electron microscopy and agarose gel electrophoresis were used to study the changes of viable bacteria number,bacterial morphology and DNA content of Aeromonas hydrophila.The results showed that when the volume ratio was 1:20 and the treatment time was 5 min,the bacteria were basically inactivated.In addition,slightly acidic electrolyzed water can cause different degrees of Aeromonas hydrophila cell damage and DNA degradation.Moreover,with the increase of volume ratio and treatment time,the degree of cell damage is gradually increased,and DNA degradation becomes more and more obvious.2.In order to study the effects of slightly acidic electrolyzed water on the intestinal enzyme activity,gill and intestine structures of carassius auratus.In this paper,slightly acidic electrolyzed water with available chlorine concentration of 3 mg/L was used to treat carassius auratus for different time,the activities of superoxide dismutase(SOD),acid phosphatase(ACP),lipase(LPS)and amylase(AMS)in intestine were measured respectively,and the gill and intestine structures were observed by paraffin section.The results showed that when the exposure time was 10 min,the activities of SOD,ACP,LPS and AMS in intestine,and the gill and intestine structures of carassius auratus were not significantly different from the control group.When the exposure time is more than 10 min,with the prolongation of exposure time,the activities of SOD and LPS were found to be increased first and then decreased,and the activities of ACP and AMS showed a trend of decreasing.The gill lamella curled up,with obvious hyperplasia of gill filaments epithelial cells,the gill lamella was wrapped completely,and some gill lamella became completely fractured.Fusion occurs between adjacent gut villi,with obvious hyperplasia of pillar cells,goblet cells and lymphocytes,complete deformation,exfoliation and necrosis of intestinal mucosal epithelial cells.In summary.It is safe to sterilize carassius auratus with slightly acidic electrolyzed water with available chlorine concentration of 3 mg/L for 10 min.3.In this paper,sodium alginate and chitosan were used as shell-materials,the Lactobacillus acidophilus,Bifidobacterium and feed were coated to prepare probiotics microcapsules feed by perforation-curing with complex coacervation composite method,and the preparation process conditions were studied.The results showed that the optimum preparation process conditions were determined as: the sodium alginate concentration 1.25%,the proportion of probiotics and sodium alginate 1:10,calcium chloride concentration 1.5%,curing time 15 min,and chitosan concentration 1.5%.Under these conditions,the particle size of probiotics microcapsules feed is uniform,ranging from 1.60 to 2.00 mm;and the encapsulation rate is reached 96.68%.Moreover,the suspension rate is 77.96% and the solubility is 13.04% after soaking in water for 12 h;and still have a survival rate of 5.2 lg(CFU/m L)after 120 min in simulated artificial gastric juice;and the embedded live bacteria can be completely released after 120 min in simulated artificial intestinal fluid,which has good floatability,water stability,acid resistance and enteric solubility.4.In order to explore the effect of inhibiting carassius auratus from infecting Aeromonas hydrophila by Lactobacillus acidophilus-Bifidobacterium probiotics microcapsules feed and slightly acidic electrolyzed water,alone or in combination.The experiment was divided into four groups: control group(basic feed),probiotic group(Lactobacillus acidophilus-Bifidobacterium probiotics microcapsules feed),slightly acidic electrolyzed water group(slightly acidic electrolyzed water treatment of infected carassius auratus)and composite method group(combination of Lactobacillus acidophilus-Bifidobacterium probiotics microcapsules feed and slightly acidic electrolyzed water).After 56 days of cultivation,all experimental carassius auratus were injected with the same amount of Aeromonas hydrophila,and then the death of carassius auratus in each group within 72 h was recorded respectively,and the survival rate was calculated.The results showed that compared with the survival rate of control group,the survival rate of slightly acidic electrolyzed water group increased by 6.66%,the survival rate of probiotic group increased by 11.66%,and the survival rate of composite method group increased by 16.66%. |
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