氨氮胁迫对中国明对虾血淋巴氨氮、尿素氮含量和抗氧化能力的影响

将600尾体重为(5.0±1.2)g的健康中国明对虾(Fenneropenaeus chinensis)随机分为5组,每组6个重复,每个重复20尾虾,分别暴露于不同氨氮质量浓度(0 mg/L、2 mg/L、4 mg/L、6 mg/L和8 mg/L)海水中,于胁迫后6 h、24 h、48 h、72 h和96 h测定血淋巴氨氮、尿素氮含量、总抗氧化能力(T-AOC)、抗超氧阴离子活力和血淋巴细胞过氧化氢酶(CAT)基因、过氧化物还原酶(Prx)基因和含半胱氨酸的天冬氨酸蛋白水解酶(caspase)基因的相对表达量,以0 mg/L氨氮组作为对照。结果显示,随着氨氮胁迫时间的延长,中国明对虾血淋巴氨氮含量逐渐积累,以8 mg/L组对虾血淋巴氨氮含量最高,是对照组的5.85倍。氨氮胁迫6 h,胁迫组中国明对虾血淋巴尿素氮含量显著高于对照组(P0.05),其中6 mg/L组对虾血淋巴尿素氮含量最高,是对照组的2.22倍。氨氮胁迫下中国明对虾血淋巴T-AOC、Prx mRNA相对表达量随着取样时间推移先升高后降低,而血淋巴抗超氧阴离子活力、CAT和caspase mRNA相对表达量随时间增加呈现先上升后下降再上升的变化过程。氨氮胁迫下中国明对虾血淋巴抗氧化能力被显著诱导,这可能破坏机体的氧化-抗氧化系统的平衡,从而导致caspase mRNA相对表达量的上调。

Effects of ambient ammonia-N exposure on hemolymph nitrogen metabolism and antioxidant capacity of Fenneropenaeus chinensis

Chinese shrimp,Fenneropenaeus chinensis,is widely cultured in China for its high economic value.However,farming yields of F.chinensis have decreased in the past few decades.The decreases in yield has been attributed to disease,as environmental deterioration due to poor management has resulted in an increased incidence of stress-induced disease.Environmental stressors,such as ammonia,have a significant effect on the antioxidant system of shrimp.However,little information is available about the effects of changes in ambient ammonia-N on hemolymph nitrogen content and antioxidant capability of Chinese shrimp.Therefore,600 shrimps initial body weight,(5.0±1.2) g] were divided randomly into five groups and exposed to water containing different concentrations of ambient ammonia-N (0 mg/L,2 mg/L,4 mg/L,6 mg/L,and 8 mg/L).Each group had six replicates of 20 shrimp each.Total antioxidant capacity (T-AOC),antisuperoxide anions,relative expression of catalase (CAT),peroxiredoxin (Prx),and caspase mRNA in hemocytes and hemolymph ammonia,and urea content were analyzed in hemolymph after exposing shrimp to different concentrations of ambient ammonia-N for 6 h,24 h,48 h,72 h,and 96 h.Shrimp cultured in filtered seawater were used as the control.The results showed that ammonia accumulated gradually in the hemolymph as exposure time increased.Hemolymph ammonia content of shrimp in the 8 mg/L group was the highest compared with that in the other groups and was 5.85 times higher than that in the control group.Hemolymph urea contents of shrimp in the ammonia-N exposed groups were higher than that in the control group after 6 h of ammonia-N exposure.The hemolymph urea of shrimp in the 6 mg/L group was the highest after 6 h and was 2.22-times higher than that in the control group.Hemolymph T-AOC and Prx mRNA expression in hemocytes of shrimp exposed to ambient ammonia-N increased initially and then decreased as exposure time increased.However,anti-superoxide anions in hemolymph and relative CAT and caspase mRNA expression levels in hemocytes increased,decreased,and then increased again as exposure time increased.The antioxidant capacity of shrimp was significantly higher after exposure to ammonia-N than that in the control.These findings demonstrate that the oxidation-antioxidant balance system in shrimp may be damaged after exposure to ammonia-N,resulting in upregulation of caspase mRNA expression.