| The factory aquaculture is an environmentally friendly,controllability,high efficiency way for aquaculture.The factory aquaculture system also known as recirculating aquaculture systems(RAS),which is gradually emerging in these years.High breeding density and over feeding is inevitable in the process of the aquatic animal farming with RAS,which lead to the generate of ammonia and nitrite.Undoubtedly,nitrite is a definite toxic substance with toxicity to aquatic animals.Many studies carried out found that aquatic animals acute exposed to nitrite can cause severe pathological changes even death.However,few studies focused on the effect of the nitrite expose and recovery afterwards on growth performance,metabolism and immunity changes of aquatic animals under factory farming conditions.Chinese perch(Siniperca chuatsi)is a carnivorous fish with great economic values,mainly distributed in the Chinese fresh water areas.It is clear that farming Chinese perch with the RAS will be the road one must follow.Study the effect of acute or chronic expose to nitrite and recovery afterwards on growth performance,metabolism and immunity changes of Chinese perch under factory farming conditions is necessary.In this study,sodium nitrite was added to the RAS,in order to simulate the rapid increasing of nitrite or the presence of nitrite of low-concentration for long-term in the RAS.After exposed to the nitrite,Chinese perch was then transferred into another RAS without additional nitrite for recovery.We aimed to provide a theoretical basis for water quality regulating and recovery treatment after nitrite expose in the process of factory farming of Chinese perch.1.Effects of acute exposure and recovery of nitrite on metabolism and immunity of Chinese perch.In this part,1 control group(T0)without exposed to nitrite,3 treatment group(T1,T24,T48)and 1 recovery group(R24)was set up.The experimental fish in T1,T24 and T48 group was exposed to 10 mg/L nitrite for 1 h,24 h and 48 h respectively.After exposed to nitrite,the experimental fish in T24 group was transferred into another RAS without additional nitrite for 24 h.Compared to T0 group,the blood methemoglobin(Met Hb)content in T1,T24 and T48 groups significant increased(P < 0.05).Glycemia levels in T1,T24 and T48 groups significant decreased(P < 0.05)while plasma lactate content in T24 and T48 groups significant increased(P < 0.05)compared to T0 group.In the liver and muscle,compared to T0 group,there were no significant changes in the glycogen and total triglycerides content(P > 0.05),while lactate content increased obviously(P < 0.05).Part of the Hb were oxidized to Met Hb,which can not carry oxygen,resulted in increasing anaerobic respiration.Compared to the T0 group,the plasma SOD and gill GSH-PX enzyme activity in the T24 group,and gill SOD enzyme activity in the T48 group significant increased(P < 0.05).In gill of T24 and T48 groups,severe lesions were observed in the through the H&E staining slice,with PAI mRNA abundance significant increased compared to T0 group(P < 0.05).In liver,infiltration of inflammatory cells was observed in T24 and T48 groups,IL-1β and PAI mRNA expression significant up-regulated in the liver and muscle of T24 group.Compared to T1,T24 and T48 group,the blood methemoglobin content,plasma,liver and muscle lactate content of R24 group significant decreased(P < 0.05)to the same level of T0group(P > 0.05).MDA level in the R24 group significant decreased compared with T0group(P < 0.05).In the R24 group,the plasma SOD enzyme activity,gill MDA content significant decreased(P < 0.05)compared with nitrite expose groups.The CAT activity in gill,SOD and CAT activity in muscle of R24 group significant increased compared to T0 group(P < 0.05).Meanwhile,the reduced pathological changes and decreased PAI mRNA expression in the gill of R24 group was observed.Infiltration of inflammatory cells in liver of the R24 group was reduced but also observable,the PAI mRNA abundance decreased to the level of T0 group(P < 0.05),while the IL-1β mRNA expression significantly higher than the T0 group(P < 0.05).The immune system of Chinese perch response frequently to nitrite expose,and completely eliminated the Oxidative stress damage.However,the damage to tissue structure can not be repaired in short time.2.The effect of chronic nitrite exposure and recovery on the growth performance,metabolism and immunity of Chinese perch.In this part,the control groups were farmed in the RAS without additional nitrite for 30 d(C30)or 60 d(C60),the nitrite exposed groups were farmed in the RAS with the sodium nitrite concentration of 0.3 mg/L for 30 d(T30)or 60 d(T60).After exposed to nitrite,part of the experimental fish were transferred into the nitrite-free RAS for a30 d recovery,the experimental fish from T30 and T60 group were named to R30 and R60 group respectively.There was no significant difference in ADG,FI,PCR observed between C30 and T30 group(P > 0.05).Compared to the C30 group,the crude protein content and protein retention(PR)in the whole body,liver and muscle of the T30 group significant decreased(P < 0.05),while the ash content of the whole body,liver and muscle significant increased(P < 0.05).In the C30 group,the BUN content in plasma significant increased(P < 0.05)compared to C30 group,while no significant changes were observed in other blood biochemical indicators(P > 0.05).The SOD,CAT and GSH-PX enzyme activity in the plasma,gill and liver of T30 group were significant up-regulated compared to C30 group.No pathological changes in the gill,liver and muscle were found via the H&E stained slice,as well as no significant changes of the expression of inflammation genes in these tissues(P > 0.05).In the R30 group,all these parameters that was significant different between the C30 and T30 group have changed obviously(P < 0.05),and no significant difference in these parameters was observed between C30 and R30 group(P > 0.05).When Chinese perch were exposed to nitrite for 30 d,the process of proteolysis increased to support the immune system,and the damage caused by nitrite expose was effectively eliminated.After a 30 d recovery,the growth performance,metabolism and immune system were restored to the normal level.Compared with the C60 group,the ADG,FI,PR,VSI and HSI significant decreased while FCR significant increased in the T60 group(P < 0.05).The cured protein and cured lipid content in whole body,liver,muscle,as well as liver glycogen content significant decreased,and ash content in whole body,liver,muscle significant increased,in the T60 group compared with C60 group.The 60 d expose to nitrite significant reduced the growth performance,and nutrients content of Chinese perch.Compared with the C60 group,the hemoglobin,glucose,total triglycerides and total cholesterol content in blood significant down-regulated(P < 0.05),while the methemoglobin,lactate,urea nitrogen,total protein,globulin,ALT and AST content in blood significant up-regulated(P < 0.05),in the T60 group.Compared with C60 group,the SOD,CAT and GSH-PX enzyme activity significant decreased(P < 0.05)while MDA content significant increased(P < 0.05),in plasma,liver and muscle.Histopathological changes were observed in the gill and liver of the T60 group,accompanied by the significant up-regulated expression of inflammatory genes(P <0.05)in gill and liver.The severe hypoxia leads to increase in anaerobic respiration and high consumption of energy substances,besides,the non-specific immune function was also impaired.After a 30 d recovery,ADG,FCR and PR were significant increased in the R60 group compared with T60 group(P < 0.05),but lower than these parameters in C60 group(P < 0.05).Except for cured lipid content in liver,cured lipid and cured protein content in all these tissue assessed significant increased(P < 0.05),but still lower than these in C60 group(P < 0.05).The BUN and globulin content in R60 group were higher than these in C60 group(P < 0.05),no significant difference was observed in other blood biochemical indexes in R06 group compare with C60 group(P > 0.05).Furthermore,the SOD,CAT and GSH-PX enzyme activity significant increased while MDA content significant decreased in the R60 group compared with T60 group(P <0.05),and histopathological changes were still observable in gill and liver.During the60 d recovery,the growth performance and nutrient deposition of Chinese perch were increased,but did not reach to the same level of control group,due to the vast of nutrients were decomposed to support the immune system. |
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