| This study used physiological,biochemical and molecular biological techniques to evaluate the effects of hypoxic stress on the physiological characteristics of triploid rainbow trout,and to explore the effects of different dietary protein and lipid levels on muscle texture,plasma stress index,hypoxic-responsive gene expression(mRNA level),antioxidant system and immune system response-related gene expression and related indicators in triploid rainbow trout after hypoxic stress.The impact of the research results will provide a theoretical basis for elucidating the molecular mechanisms and regulation strategies of fish hypoxic stress.This study consists of three parts.1.Effects on triploid rainbow trout after hypoxic stress.In this study,the effects of hypoxic stress(dissolved oxygen below 5 mg/L for 10 min)on muscle texture,blood physiological parameters,antioxidant system and related gene expression of triploid rainbow trout were investigated by setting normal and stress groups.The results showed that:(1)Hypoxic stress leads to decreased muscle texture.The pH,cohesiveness,springiness,gumminess and chewiness of the muscles in the stress group were significantly higher than those in the normal group(P<0.05),and the water holding capacity and brightness value(L*),red value(a*)and yellow value(b*)and adhesiveness were significantly lower than normal group(P<0.05).(2)Hypoxic stress leads to significant changes in plasma stress-related indicators,plasma alanine aminotransferase(ALT),aspartate aminotransferase(AST),lactate dehydrogenase(LDH)and phosphocreatine kinase(CK)activity and globulin(GLOB)after hypoxic stress Glucose(GLU)and triglyceride(TG)and cortisol levels were significantly higher than the normal group(P<0.05);albumin(ALB)was significantly lower than the normal group(P<0.05),there were no significant difference in plasma total protein(TP),total cholesterol(TC)and alkaline phosphatase(ALP)before and after stress(P>0.05).(3)Hypoxic stress leads to significant changes in hypoxia-related gene expression.The expression levels of hypoxia-inducible factor 1?(HIF-1?)gene was up-regulated in muscle,and the expression levels of heme oxygenase 1(HO-1)gene was down-regulated in the liver.(4)Hypoxic stress causes the antioxidant system to be significantly activated,the content of malondialdehyde(MDA)in plasma and liver of stress group was significantly higher than that of normal group(P<0.05),the total antioxidant capacity of plasma and liver in stress group(T-AOC)was significantly lower than the normal group(P<0.05).The expression levels of superoxide dismutase(SOD)gene and catalase(CAT)gene mRNA in muscle tissue was up-regulated under hypoxic stress,and the expression levels of nuclear factor erythrocyte 2(NF-E2)-related factor 2(Nrf2)gene mRNA was up-regulated in liver tissue,while the expression level of SOD gene mRNA was down-regulated.(5)Hypoxic stress causes the immune system to be significantly activated,the activity of lysozyme and heat shock protein(HSP70)in plasma was significantly increased after stress(P<0.05),the expression levels of HSP70 mRNA was up-regulated in muscle,the expression levels of HSP70 and tumor necrosis factor alpha(TNF?)gene mRNA were down-regulated in liver tissues.In summary,the hypoxic stress method used in this experiment has a significant effect on the physiological state of triploid rainbow trout,which causes the muscle quality of triploid rainbow trout to be reduced and the antioxidant system and immune system to be activated.2.The effect of dietary protein levels on hypoxic stress in triploid rainbow trout.The initial body weight of triploid rainbow trout was(233.30±0.39)g,and three isoenergetic and isolipidic diets were formulated in this study,which are 35.40% protein level(low dietary protein group),43.30% protein level(medium dietary protein group)and 52.4%protein level(high dietary protein group).After 80 days growth test,acute hypoxic stress(dissolved oxygen was less than 5 mg/L for 10 min).The results showed that muscle red value and brightness value decreased,The levels of GLU in plasma decreased in high dietary protein group(P<0.05).Muscle adhesiveness and red values decreased,the levels of ALT,AST,ALP,LDH and TC in plasma increased in the low dietary protein group(P<0.05).The levels of T-AOC in plasma was elevated(P<0.05),the expression levels of Nrf2 gene was up-regulated in liver and muscle,the expression levels of TNF? and IL-1? gene were up-regulated in muscle,and the expression levels of IL-8 gene was down-regulated in medium dietary protein group.The expression levels of TNF?,HSP70,IL-1? and IL-8 gene in the liver of the middle dietary protein group were lower than those in the high dietary protein group.Therefore,low or high dietary protein levels will aggravate liver stress damage,and optimal dietary protein levels(43.30%)help to increase muscle redness and anti-stress ability,and alleviate hypoxic stress damage.3.The effect of dietary lipid levels on hypoxic stress in triploid rainbow trout.The initial body weight of triploid rainbow trout was(232.83±0.44)g,and four isonitrogenous diets were formulated in this study,which are 6.60% lipid level(low dietary lipid group),14.80% lipid level(medium-low dietary lipid group),22.80% lipid level(medium-high dietary lipid group)and 29.4% lipid level(high dietary lipid group).After 80 days growth test,acute hypoxic stress(dissolved oxygen was less than 5 mg/L for 10 min).The results showed that muscle red and yellow values were reduced,and the levels of ALT,AST,and LDH in plasma were elevated in the low dietary lipid group(P<0.05).The levels of TC and MDA in plasma increased(P<0.05),and T-AOC decreased in the high dietary lipid group.The expression level of SOD gene in the liver of triploid rainbow trout was up-regulated in the medium-high dietary lipid group.The levels of TP,ALB and GLOB in plasma decreased in the low fat group.The expression levels of HSP-70 and IL-8 gene in the muscle of triploid rainbow trout were up-regulated in low and high dietary lipid groups.Therefore,low or high dietary lipid levels affect the muscle texture of triploid rainbow trout,which will aggravate the metabolic burden of triploid rainbow trout under hypoxic stress.Optimal dietary lipid levels(22.80%)will help to respond to hypoxic stress damage and enhance immunity.In summary,hypoxic stress can significantly reduce the muscle texture of triploid rainbow trout.The antioxidant system and immune system of the triploid rainbow trout are activated,high or low dietary protein levels and lipid levels lead to adverse effects on the antioxidant system and immune system of triploid rainbow trout.Optimal dietary protein level(43.30%)and dietary lipid level(22.80%)can alleviate the effects of hypoxic stress on the antioxidant system and immune system of triploid rainbow trout. |
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