急性盐度胁迫对摄食不同镁水平饲料鲈血清渗透压和离子水平以及鳃丝ATP酶活力的影响

为研究饲喂不同镁水平饲料后,鲈血清渗透压、离子水平和鳃丝ATP酶活力对急性盐度胁迫的反应,实验用镁水平为0.413 g/kg(D1,对照组)、1.042 g/kg(D2)、1.577 g/kg(D3)、1.991 g/kg(D4)的4种实验饲料,分别投喂初始平均体质量为(30±0.5)g的鲈。实验鱼在淡水循环养殖系统中饲养50 d后立即转入海水循环养殖系统,并在转入前(0 h)和转入后1、3、6、12、24 h分别采集鲈鳃丝和血液样本。结果显示:盐度胁迫前饲料镁水平对鲈血清渗透压、Na+、K+、Cl-、Mg2+含量和鳃丝中Na+/K+-ATP(NKA)与Ca2+/Mg2+-ATP(CMA)酶的活力有显著影响(P<0.05),其中血清渗透压、Mg2+含量和NKA酶活力随饲料镁水平的增加而升高。D4组的血清渗透压、Mg2+含量、NKA和CMA酶活力显著高于其他组(P<0.05),表明该组鲈处于高强度的渗透压调节的生理状态。急性盐度胁迫中,血清Na+和Cl-含量随胁迫时间的延长呈逐渐上升趋势,血清渗透压、K+、Ca2+、Mg2+和鳃丝ATP酶活力在0～24 h内呈波动性变化。D1组的NKA和CMA酶活力在胁迫1 h时显著低于其他组(P<0.05),表明长期摄食低镁水平的饲料会降低鲈鳃丝NKA和CMA酶对环境盐度刺激的敏感度。研究表明,淡水养殖鲈的饲料中镁水平应低于1.991 g/kg,以减少维持鳃丝NKA与CMA酶高活力而导致的能量损失,而在环境由低盐向高盐的快速转变过程中,较高的饲料镁水平可通过快速提高的鳃丝NKA与CMA酶活力而有利于鲈快速适应高盐环境。

Effects of acute salinity stress on the serum osmolality,serum ion concentrations,and ATPase activity in gill filaments of Japanese seabass(Lateolabrax japonicus)fed with diets containing different magnesium levels

An acute salinity stress trial was conducted to estimate the effect of dietary magnesium level on serum osmolality,serum ions and ATP enzyme in gill filaments of Japanese seabass Lateolabrax japonicus.Four semi-purified diets were formulated containing 0.413 g(D1),1.042 g(D2),1.577 g(D3),1.991 g(D4)magnesium(as magnesium sulphate)per kilogram diet to feed triplicate groups of fishinitial average weight(30±0.5)g]in freshwater circulation system for 50 days.Then all fish were transferred from freshwater to seawater to collect the serum and gill filaments at 0,1,3,6,12,24 h,respectively.The results showed that dietary magnesium levels significantly affected the levels of serum ions(Na+,Cl-,K+,Mg2+),serum osmolality and the activities of Na+/K+-ATPase(NKA)and Ca2+/Mg2+-ATPase(CMA)in gill filaments at 0 h(P<0.05).The serum osmolality,serum Mg2+ and NKA of gill filaments increased with the increase of dietary magnesium levels.The levels of serum Mg2+ and osmolality,NKA and CMA activities in gill filaments of fish fed D4 were significantly higher than those fed the other diets(P<0.05),which indicated the Japanese seabass fed D4 was in a state of high intensity osmotic pressure regulating.During the salinity stress periods,the contents of serum Na+ and Cl-increased with the time extension of salinity stress,while the levels of serum osmolality,K+,Ca2+ and Mg2+,NKA and CMA activities fluctuated with stress duration from 0 to 24 h.NKA and CMA activities of fish fed D1 were significantly lower than those of other groups,which indicated it would reduce the sensitivities of NKA and MKA in gill filaments to salinity stimulation for Japanese seabass fed low magnesium level diet for 50 d.The results suggested that in order to reduce energy consumption for higher activities of NKA and CMA in gill,dietary magnesium level should be lower than 1.991 g/kg for Japanese seabass cultured in freshwater,however,high dietary magnesium levels improve NKA and CMA activities in gill,which could be beneficial to quick adaptation high salinity environment for Japanese seabass transferred from low salinity water into high salinity water.