Research On Stress Relieving Techniques Of Channel Catfish Fry (Ictalurus Punctatus) In Transport

Ictalurus punctatus is a kind of warm-water freshwater economic fish with high protein,low fat,high nutrition value,short growth cycle and cultured yield.The breeding base of channel catfish in China is mainly concentrated in the Yangtze River basin due to factors such as climate and biological characteristics,while the breeding areas are distributed in many provinces across the country.The existing seedling transportation technology is established by the industry practitioners based on experience,and there are problems such as significant reduction of survival rate after long time transportation and rough control of temperature and water quality,which can easily lead to seedling transportation losses.Therefore,in this study,Ictalurus punctatus fry were studied to optimize key technologies such as domestication conditions,anti-stress agent screening and application for transportation procedures of major transport size fry(fry and juvenile).The main research results are as follows:(1)Taurine,vitamin C,vitamin E,glutamine and monosodium glutamate all alleviated the stress response of juvenile channel catfish during the simulated transport.During the simulated transport for 14 h,compared with the control group,the addition of five additives to transport reduced the water ammonia nitrogen content and increased the p H value of water,decreased the energy metabolism indicators of juvenile channel catfish(Cortisol(COR),Glucose(GLU),Lactate dehydrogenase(LDH)),and significantly changed the activity of Catalase(CAT),Malondialdehyde(MDA)content,and total antioxidant capacity(T-AOC)to resist oxidative stress.The histopathological results showed that the additive group protected the gill and skin tissue structures better compared to the control group.The optimal concentration of Taurine,vitamin C,vitamin E,glutamine and sodium glutamate was 70 mg/L,40mg/L,18 mg/L,20 mg/L and 0.6 mg/L respectively.The best transportation effect is achieved by adding 40%and 80%of the optimal amount of five additives into a composite additive.(2)Pre-transport domestication with a fish-to-water ratio of 1:4(g/L)and a temperature of 19°C,respectively,both significantly reduced the stress caused by juvenile channel catfish during simulated transport and improved transport water quality(reduced ammonia content and stabilized p H).Compared with the control group,the experimental group showed reduced serum levels of COR and GLU,reduced activities of LDH,CAT,SOD and malondialdehyde in liver tissues,and a smaller degree of structural damage to the skin and intestine.(3)The salt bath of sodium chloride at a mass concentration of 5‰for 30 min in juvenile channel catfish could effectively improve their anti-stress ability.After 12 h of simulated transport,compared with the control group,the serum levels of COR and GLU in the experimental group were reduced and the balance of Na~+and K~+was maintained;LDH,CAT,SOD activity and MDA content in liver tissues were reduced;Na~+/K~+-ATPase activity in gill tissues was reduced;and the degree of damage to gill,skin and intestinal structures was less.The integrated biomarker(IBR)model analysis showed that the lowest IBR index was observed at a salt bath concentration of 5‰.(4)Glucose,Taurine,vitamin C and penicillin G sodium all alleviated the stress response of channel catfish fry during simulated transportation.After 27 hours of simulated transportation,the water quality parameters of the control group showed significant changes,with an increase in total ammonia nitrogen,carbon dioxide,osmoregulated ions(sodium,potassium,calcium),and COR,while a decrease in p H and dissolved oxygen.The water quality of the additive group was better than that of the control group after transportation.The histopathological results showed that the skin of the control group showed varying degrees of damage,while the skin of the additive group showed relatively small damage.There were significant changes in the levels of COR,GLU,and biomarkers(MDA,SOD,T-AOC,Na~+/K~+-ATP,and CAT)in the transport group(control group and additive group).The IBR index of the additive group was lower than that of the control group,and the IBR index of 4 mg/L penicillin G sodium was the lowest,with the highest survival rate after 27 hours of simulated transportation.