The Effect of Corona Dormancy on the Physiological Stress and Main Nutritional Components in the Transport of Trachinotus ovatus During Survival
The golden pomfret(Trachinotus ovatus)is distributed in tropical and subtropical waters such as those of the East China Sea,South China Sea,and the Chinese Yellow and Bohai Seas.The golden pomfret grows rapidly and is the most modernized and intensive marine aquaculture fish in China.Furthermore,the golden pomfret is also the preferred variety of fish for expanding sea aquaculture spaces.Presently,the market mainly includes three methods:Freezing,processing,and live sales.If fish can be processed in multiple ways while maintaining freshness,fresh fish is the best choice.However,the existing transportation of live fish suffers from various problems such as low survival rate,nutrient loss,and short transportation time due to stress,hypoxia,and water quality deterioration.T ovatus is a warm temperature-loving,omnivorous migratory fish with high oxygen consumption and vigorous metabolism.Fishing exerts high stress on the organism,and they easily die in low temperature environments(＜13 ℃).The difficulty of keeping the fish alive and transporting is also the main reason live fish are difficult to find in markets.To solve the above problems,chemical anesthesia,physical dormancy,and other methods are generally used to improve the survival rate of fish and maintain good nutritional quality in the process of keeping them alive and for transportation.Chemical anesthesia may pose risks of drug residue,and there are certain restrictions on the drug withdrawal period for the fish to be transported alive.Among the physical dormancy methods,the ecological ice temperature induced dormancy method is widely used,but it needs low temperature acclimation before treatment,which consumes long time periods.Therefore,an efficient,green and safe way of keeping alive transportation technology is particularly urgent,and corona dormancy presents an environment friendly,safe,new,and efficient way of physical dormancy that meets consumer needs,with broad application prospects.Chemical anesthesia and low temperature-induced dormancy are mostly used in the pretreatment technology of survival and transportation of marine fish,while the research on corona dormancy technology is less,and the research and application of corona dormant T.ovatus have not been reported locally or abroad.In this study,T.ovatus were placed in an electric shock box after 6 h of temporary rearing.The T.ovatus were shocked by pulsed DC currents.The recovery phase was recorded by stages through behavioral observation.The optimal treatment conditions of pulsed DC corona dormancy were optimized by using the dormancy rate,dormancy time,72 h survival rate and survival time as evaluation indexes through single factor and orthogonal experiments,and the biochemical parameters of serum,brain tissue,muscle and liver are determined indexes of oxidative stress,metabolism,and basic nutrients.The results showed that under the conditions of 20 ℃ water temperature,140 V voltage,and 4 s treatment time,the dormancy rate and 72 h survival rate of fish could reach 100％,and the survival time was(165.6±42.7)h.After corona dormancy treatment,the contents of glucose(GLU),glutamic oxaloacetic transaminase(GOT),and cortisol(COR)in fish serum significantly increased(P＜0.05),and return to normal levels within 4-12 hours of survival,indicating that electrical stimulation can make the life activities of fish become violent,resulting in the rise of stress indicators in a short time.The content of heat shock protein 70(Hsp70),glutathione S-transferase(GST-S)activity,and catalase(CAT)activity in liver and brain tissues significantly increased(P＜0.05),while the content of malondialdehyde(MDA)in brain tissues was significantly decreased compared with that in the control group within 4-72 hours(P＜0.05),indicating that the technology can improve the tolerance of fish to environmental stress and reduce the degree of brain damage,reduce the lipid peroxidation in the brain and the accumulation of hydrogen peroxide in the liver,so as to reduce the damage cause by environmental stress and short-term damage to tissues.The content of liver glycogen(Gly)show a downward trend during the preservation process,while the content of lactic acid(LD)in liver and muscle increase significantly(P＜0.05),indicating that anaerobic metabolism occurs during the preservation process of fasting,which consume glycogen and produced lactic acid.Crude ash,protein,and fat in fish meat show a downward trend during the preservation process,with the crude fat content decreased the most significantly(P＜0.05),and the proportion of decline in the experimental group was reduced compared with that of the control group.The research shows that the appropriate conditions of pulsed DC can induce the dormancy of T.ovatus,and after corona dormancy fish exhibit less stress in the face of external factors.From the index point of view,the technology can improve the release of Hsp70 and the activity of antioxidant enzymes to slow the stress response of the fish under survival stress,reduce tissue damage,and maintain a low metabolic level after survival,reducing the consumption of inorganic matter,fat,and protein.Thus,the efficiency and quality in the process of keeping alive transportation are improving,which is convenient for breeding and transportation.Finally,these findings lay a theoretical foundation for maintaining the vitality and quality of T.ovatus.
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