Wood C M, Wilson R W, Gonzalez R J, Patrick M L, Bergman H L, Narahara A, Val A L
Department of Aquaculture, National Institute for Amazon Research (Instituto Nacional de Pesquisas da Amazonia), Alameda Cosme Ferreira, Manaus, Amazonas, Brazil.
Physiol Zool. 1998 Nov-Dec;71(6):658-70. doi: 10.1086/515977.
Our goal was to compare the internal physiological responses to acid challenge in an acidophilic tropical teleost endemic to dilute low-pH waters with those in nonacidophilic temperate species such as salmonids, which have been the subjects of most previous investigations. The Amazonian tambaqui (Colossoma macropomum), which migrates between circumneutral water and dilute acidic "blackwater" of the Rio Negro, was exposed to a graded low-pH and recovery regime in representative soft water (Na+ = 15, Cl- = 16, Ca2+ = 20 mumol L-1). Fish were fitted with arterial catheters for repetitive blood sampling. Water pH was altered from 6.5 (control) to 5.0, 4.0, 3.0, and back to 6.5 (recovery) on successive days. Some deaths occurred at pH 3.0. Throughout the regime, there were no disturbances of blood gases (O2 and CO2 tensions and contents) or lactate levels, and only very minor changes in acid-base status of plasma and red cells. However, erythrocytic guanylate and adenylate levels increased at pH's less than or equal to 5.0. Down to pH 4.0, plasma glucose, cortisol, and total ammonia levels remained constant, but all increased at pH 3.0, denoting a stress response. Plasma Na+ and Cl- levels declined and plasma protein concentration increased at pH 3.0, indicative of ionoregulatory and fluid volume disturbance, and neither recovered upon return to pH 6.5. Cortisol and ammonia elevations also persisted. Transepithelial potential changed progressively from highly negative values (inside) at pH 6.5 to highly positive values at pH 3.0; these alterations were fully reversible. Experimental elevations in water calcium levels drove the transepithelial potential positive at circumneutral pH, attenuated or prevented changes in transepithelial potential at low pH, and reduced Na+ and Cl- loss rates to the water during acute low-pH challenges. In general, tambaqui exhibited responses to low pH that were qualitatively similar but quantitatively more resistant than those previously documented in salmonids.
我们的目标是比较一种稀酸低pH值水域特有的嗜酸性热带硬骨鱼与非嗜酸性温带物种（如鲑科鱼类，此前大多数研究的对象）对酸挑战的内部生理反应。亚马逊坦巴基鱼（巨脂鲤）在中性水域和里奥内格罗河的稀酸“黑水”之间洄游，将其置于具有代表性的软水中（Na+ = 15，Cl- = 16，Ca2+ = 20 μmol L-1），使其经历逐渐降低pH值然后恢复的过程。给鱼安装动脉导管以便重复采集血液样本。在连续几天内，将水的pH值从6.5（对照）依次改变为5.0、4.0、3.0，然后再回到6.5（恢复）。在pH值为3.0时出现了一些死亡情况。在整个过程中，血液气体（氧气和二氧化碳张力及含量）或乳酸水平没有受到干扰，血浆和红细胞的酸碱状态仅有非常轻微的变化。然而，当pH值小于或等于5.0时，红细胞鸟苷酸和腺苷酸水平升高。在pH值降至4.0时，血浆葡萄糖、皮质醇和总氨水平保持恒定，但在pH值为3.0时均升高，表明出现了应激反应。在pH值为3.0时，血浆Na+和Cl-水平下降，血浆蛋白浓度升高，表明存在离子调节和体液量紊乱，并且在恢复到pH值6.5时均未恢复。皮质醇和氨水平升高的情况也持续存在。跨上皮电位从pH值6.5时的高度负值（内部）逐渐变为pH值3.0时的高度正值；这些变化是完全可逆的。实验性提高水中钙水平会使跨上皮电位在中性pH值时变为正值，减弱或阻止低pH值时跨上皮电位的变化，并在急性低pH值挑战期间降低Na+和Cl-向水中的流失率。总体而言，坦巴基鱼对低pH值的反应在性质上与之前在鲑科鱼类中记录的反应相似，但在数量上更具耐受性。
