Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, BE-2020 Antwerp, Belgium.
Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, BE-2020 Antwerp, Belgium.
Aquat Toxicol. 2015 Mar;160:39-56. doi: 10.1016/j.aquatox.2015.01.005. Epub 2015 Jan 8.
We investigated the interactive effect of ammonia toxicity, salinity challenge and nutritional status on the ecophysiological performance of European sea bass (Dicentrarchus labrax). Fish were progressively acclimated to normal seawater (32ppt), to brackish water (20ppt and 10ppt) and to hyposaline water (2.5ppt). Following acclimation to different salinities for two weeks, fish were exposed to high environmental ammonia (HEA, 20mg/L ∼1.18mM representing 50% of 96h LC50 value for ammonia) for 12h, 48h, 84h and 180h, and were either fed (2% body weight) or fasted (unfed for 7 days prior to HEA exposure). Biochemical responses such as ammonia (Jamm) and urea excretion rate, plasma ammonia, urea and lactate, plasma ions (Na(+), Cl(-) and K(+)) and osmolality, muscle water content (MWC) and liver and muscle energy budget (glycogen, lipid and protein), as well as branchial Na(+)/K(+)-ATPase (NKA) and H(+)-ATPase activity, and branchial mRNA expression of NKA and Na(+)/K(+)/2Cl(-) co-transporter (NKCC1) were investigated in order to understand metabolic and ion- osmoregulatory consequences of the experimental conditions. During HEA, Jamm was inhibited in fasted fish at 10ppt, while fed fish were still able to excrete efficiently. At 2.5ppt, both feeding groups subjected to HEA experienced severe reductions and eventually a reversion in Jamm. Overall, the build-up of plasma ammonia in HEA exposed fed fish was much lower than fasted ones. Unlike fasted fish, fed fish acclimated to lower salinities (10ppt-2.5ppt) could maintain plasma osmolality, [Na(+)], [Cl(-)] and MWC during HEA exposure. Thus fed fish were able to sustain ion-osmotic homeostasis which was associated with a more pronounced up-regulation in NKA expression and activity. At 2.5ppt both feeding groups activated H(+)-ATPase. The expression of NKCC1 was down-regulated at lower salinities in both fed and fasted fish, but was upregulated within each salinity after a few days of HEA exposure. Though an increment in plasma lactate content and a decline in energy stores were noted for both feeding regimes, the effect was more severe in feed deprived fish. Overall, several different physiological processes were disturbed in fasted sea bass during HEA exposure while feeding alleviated adverse effects of high ammonia and salinity challenge. This suggests that low food availability can render fish more vulnerable to external ammonia, especially at reduced seawater salinities.
我们研究了氨毒性、盐度挑战和营养状况对欧洲鲈鱼（Dicentrarchus labrax）生态生理学性能的交互影响。鱼逐渐适应正常海水（32ppt）、半咸水（20ppt 和 10ppt）和低盐度水（2.5ppt）。在适应不同盐度两周后，鱼暴露于高环境氨（HEA，20mg/L∼1.18mM，代表氨的 96hLC50 值的 50%）12h、48h、84h 和 180h，并进行投喂（体重的 2%）或禁食（在暴露于 HEA 前禁食 7 天）。为了了解实验条件下的代谢和离子渗透压调节后果，研究了氨（Jamm）和尿素排泄率、血浆氨、尿素和乳酸、血浆离子（Na+、Cl-和 K+）和渗透压、肌肉水分含量（MWC）以及肝和肌肉能量预算（糖原、脂质和蛋白质）、鳃 Na+/K+-ATP 酶（NKA）和 H+-ATP 酶活性以及鳃 NKA 和 Na+/K+/2Cl-协同转运蛋白（NKCC1）的 mRNA 表达。在 HEA 期间，10ppt 下禁食鱼的 Jamm 受到抑制，而摄食鱼仍能有效排泄。在 2.5ppt 时，两组暴露于 HEA 的摄食鱼均经历了 Jamm 的严重减少，最终出现逆转。总的来说，暴露于 HEA 的摄食鱼的血浆氨积累要低于禁食鱼。与禁食鱼不同，适应低盐度（10ppt-2.5ppt）的摄食鱼在暴露于 HEA 期间能够维持血浆渗透压、[Na+]、[Cl-]和 MWC。因此，摄食鱼能够维持离子渗透压稳态，这与 NKA 表达和活性的更明显上调有关。在 2.5ppt 时，两组摄食鱼均激活了 H+-ATP 酶。在较低盐度下，NKCC1 的表达在摄食和禁食鱼中均下调，但在 HEA 暴露几天后，在每种盐度下均上调。尽管两种摄食方式的血浆乳酸含量增加和能量储存减少，但在禁食鱼中更为严重。总的来说，在 HEA 暴露期间，禁食鲈鱼的几种不同生理过程受到干扰，而摄食则减轻了高氨和盐度挑战的不利影响。这表明，低食物可利用性会使鱼类更容易受到外部氨的影响，尤其是在降低的海水盐度下。
