碳酸盐碱度胁迫对尼罗罗非鱼血清pH、游离氨浓度及相关基因表达的影响

【目的】了解碳酸盐碱度对罗非鱼的毒性及其相应耐受机制,为耐盐碱罗非鱼育种及生产应用提供理论指导。【方法】将尼罗罗非鱼从淡水直接转入4个碳酸盐碱度处理(4.0、6.0、8.0和10.0g/LNaHCO_3)中进行急性胁迫试验,利用pH计、紫外分光光度计及荧光定量PCR,分别检测胁迫0.5、1.0、4.0、6.0、9.0、12.0、18.0、24.0、36.0和48.0h的罗非鱼血清pH、游离氨浓度及肾组织中碳酸酐酶(CA)和谷氨酰胺合成酶(GS)基因的相对表达量。【结果】在各碳酸盐碱度处理组中,胁迫1.0h后罗非鱼的血清pH、游离氨浓度均发生显著变化(P0.05)。经4.0和6.0g/L碳酸盐碱度胁迫48.0h后未出现死鱼现象,其血清pH、游离氨浓度及CA基因、GS基因的表达量均呈先升高再降低的变化趋势;经8.0g/L碳酸盐碱度胁迫9.0h后陆续出现死鱼现象,血清pH高达8.11、游离氨浓度为486.28μmol/L,至胁迫12.0h后罗非鱼全部死亡;经10.0g/L碳酸盐碱度胁迫出现死鱼的时间明显早于8.0g/L碳酸盐碱度胁迫,胁迫1.0h后其血清pH达8.14、游离氨浓度为365.89μmol/L,胁迫4.0h后罗非鱼全部死亡。【结论】尼罗罗非鱼能耐受的血清pH上限在8.10附近,耐受的游离氨浓度为525.66μmol/L。在低碳酸盐碱度(小于6.0g/L)胁迫下,尼罗罗非鱼可通过生理调控血清pH和游离氨浓度而适应胁迫逆境,且CA和GS参与了相应离子的转运及氨氮代谢。

Effects of carbonate alkalinity on serum pH,ammonia concentration and related gene expression in Oreochromisniloticus

Objective]In order to provide theoretical basis for breeding , production and application of alkalinity-to-lerant tilapia strains, the toxicity of carbonate alkalinity to Oreochromis niloticus and corresponding mechanism of alkalinity tolerance were studied. Method]O. niloticus individuals were divided into four groups and directly transferred into carbo-nate alkalinity treatments(4.0, 6.0, 8.0 and 10.0 g/L NaHCO3) from freshwater for acute stress. The serum pH, ammonia concentration and relative expression of carbonic anhydrase(CA) gene and glutamine synthetase(GS) gene in kidney were determined using pH meter, UV spectrophotometer and quantitative real-time PCR post-transfer at 0.5, 1.0, 4.0, 6.0, 9.0, 12.0, 18.0, 24.0, 36.0 and 48.0 h, respectively. Result]In all treatment groups, the serum pH and ammonia concentration changed significantly after 1.0 h(P<0.05). In 4.0 and 6.0 g/L NaHCO3 treatment groups, no dead fish was found within 48.0 h, and the serum pH, ammonia concentration, relative expression of CA and GS genes showed “up-peak-down” change trend. In 8.0 g/L NaHCO3 treatment group, dead fishes were found in succession after 9.0 h, and the corresponding serum pH and ammonia concentration was 8.11 and 486.28 μmol/L, respectively, all fishes were dead after 12.0 h. In 10.0 g/L NaHCO3 treatment group, dead fishes were found earlier than those in 8.0 g/L NaHCO3 treatments, and the serum pH and ammonia concentration were 8.14 and 365.89 μmol/L after 1.0 h, respectively, all fishes were dead after 4.0 h. Conclusion]O. niloticus can tolerate a serum pH of up to 8.10 and ammonia concentration of at least 525.66μmol/L. O. niloticus can adapt to alkalinity water to a certain degree in less than 6.0 g/L NaHCO3 though regulation of pH and ammonia, and CA and GS are involved in ion transportations and nitrogen metabolism under alkalinity stress.