低浓度氨氮预适应后高氨氮暴露对黄颡鱼鳃组织结构、免疫指标及相关基因的影响

HIGH AMMONIA EXPOSURE AFTER PRE-ACCLIMATIZATION TO LOW AMMONIA CONCENTRATION ON GILL TISSUE STRUCTURE,IMMUNE INDICES,AND RELATED GENES IN TACHYSURUS FULVIDRACO

研究旨在研究低浓度氨氮预适应后高浓度氨氮暴露对黄颡鱼(Tachysurus fulvidraco)鳃组织结构、免疫指标及相关基因的影响。将黄颡鱼[体重:(3.13±0.49)g]分别暴露于低浓度氨氮(4.7 mg/L,10%96h LC50)中预先适应3d、7d、14d后,在高浓度氨氮(23.7 mg/L,50%96h LC50)暴露12h和48h。结果显示:(1)在高浓度氨氮胁迫48h后,不同时长低浓度氨氮预适应组(3d、7d、14d)和对照组(未经过低浓度氨氮预适应)鳃组织细胞出现空泡化,鳃小片变短、卷曲、合并等不同程度的病理变化;但低浓度氨氮预适应组的鳃组织在高浓度氨氮暴露12h和48h时损伤程度均低于对照组,且预适应14d组在高浓度氨氮暴露12h和48h时鱼的鳃组织损伤程度最小。(2)在高浓度氨氮胁迫48h后,预适应组和对照组的黄颡鱼体内LZM活性和IgM、C3、C4含量呈现一定的升高;所有预适应组的LZM活性和IgM、C3含量显著升高,C4含量则只有预适应7d和14d显著升高。高浓度氨氮胁迫12h时,预适应14d组的LZM活性和C3、C4含量均显著高于其他组(P<0.05)。(3)在高浓度氨氮胁迫12h时,tnf-α和c3基因表达水平显著下调;il-1β基因表达水平无显著变化;仅预适应7d组igm基因表达水平的显著上调。上述结果表明,经过低浓度氨氮预适应后高浓度氨氮暴露,黄颡鱼鳃组织损伤程度降低,LZM活性和IgM、C3、C4含量升高,黄颡鱼在低浓度氨氮预适应后对高浓度氨氮环境具有一定的耐受能力。

Ammonia nitrogen is an important water quality indicator in fish culture,as concentrations exceeding the safe range can cause stress to fish.The study aimed to investigate the effects of high ammonia exposure on the gill tissue structure,immune indexes,and related genes of yellow catfish(Tachysurus fulvidraco)after pre-acclimatization with low ammonia concentration.Yellow catfish[body weight:(3.13±0.49)g]were exposed to low concentration of ammonia nitrogen(4.7 mg/L,10%96h LC50)after pre-acclimated for 3,7,and 14d,followed by exposure to high ammonia nitrogen concentrations(23.7 mg/L,50%96h LC50)for 12h and 48h,respectively.The results showed that:(1)after 48h of high ammonia nitrogen stress,the gill structure of yellow catfish displayed various pathological changes such as vacuolization,shortening,curling,and merging of gill lamellae.However,the pre-acclimated groups(3d,7d,and 14d)experienced less damage compared to the control group(not pre-acclimated to the low concentration of ammonia nitrogen).The control group showed different pathological changes such as vacuolization,gill lamellae shortening,curling,and merging.In contrast,the gill tissues of the pre-acclimated group were less damaged at both 12h and 48h of exposure to the high concentration of ammonia nitrogen.Specifically,the 14d pre-acclimated group exhibited the least gill tissue damage at these time points.(2)After 48h of high-concentration ammonia nitrogen stress,the LZM activity and IgM,C3 and C4 contents of yellow catfish increased to varying degrees in both pre-adapted and control groups.In all pre-adapted groups,the LZM activity and IgM,C3 contents showed significantly increased,while C4 contents were only significantly increased only in the pre-adapted 7d and the 14d group.At 12h of high-concentration ammonia nitrogen stress,the LZM activity and C3,C4 contents in the 14d group were significantly increased.Additionally,the LZM activity and C3,C4 contents of the 14d group were significantly increased.C3 and C4 contents were significantly higher than those of other groups at 12h of high concentration ammonia stress(P<0.05).(3)The expression levels of tnf-α and c3 genes were significantly down-regulated at 12h of high ammonia nitrogen stress,while in the expression level of il-1β gene showed no significant change.The expression level of igm gene was significantly upregulated only in the 7d pre-acclimatization group.The above results indicated that pre-acclimatization to low concentrations of ammonia nitrogen,followed by exposure to high concentration of ammonia nitrogen,resulted in reduced gill tissue damage,increased LZM activity,and elevated IgM,C3 and C4 contents in yellow catfish.This suggests that yellow catifish develop a certain tolerance to high concentrations of ammonia nitrogen after pre-acclimatization to low concentration of ammonia nitrogen.