Piermarini P M, Evans D H
Department of Zoology, University of Florida, Gainesville 32611, USA.
Physiol Zool. 1998 Sep-Oct;71(5):553-60. doi: 10.1086/515973.
The goals of this study were to (1) measure plasma osmolytes and rectal gland weights of a freshwater (FW) Atlantic stingray (Dasyatis sabina) population in the St. Johns River, Florida, and (2) determine how these parameters change after acclimation to seawater (SW). We hypothesized that the FW D. sabina may show physiological divergence from marine D. sabina, because the FW individuals reproduce and complete their life cycle in the St. Johns River. The FW D. sabina hyperregulate their plasma osmolality (621.4 mOsm kg(-1)), with plasma Na+, Cl-, and urea concentrations of 211.9, 207.8, and 195.9 mmol L(-1), respectively. FW D. sabina were exposed to 100% SW for 8 d, and their hematocrit did not change significantly compared to control animals left in FW. However, plasma osmolality increased significantly (953 mOsm kg(-1)), with significant increases in plasma concentrations of Na+, Cl-, and urea to 319.13, 296.1, and 329.76 mmol L(-1), respectively. The plasma of the SW-adapted D. sabina was hypo-osmotic and hypoionic to 100% SW. Rectal gland weight to body weight (RGBW) ratios of FW D. sabina were about 80% lower than RGBW ratios reported for marine D. sabina; the RGBW ratio did not increase significantly after SW acclimation. This may indicate that branchial and renal mechanisms are also involved with ion excretion. We conclude that the FW D. sabina are physiologically euryhaline and have not evolved the osmoregulatory strategy of stenohaline FW Potamotrygonid stingrays.
（1）测量佛罗里达州圣约翰斯河中淡水（FW）大西洋黄貂鱼（Dasyatis sabina）种群的血浆渗透溶质和直肠腺重量；（2）确定这些参数在适应海水（SW）后如何变化。我们假设淡水D. sabina可能与海洋D. sabina表现出生理差异，因为淡水个体在圣约翰斯河繁殖并完成其生命周期。淡水D. sabina的血浆渗透压过高（621.4 mOsm kg⁻¹），血浆Na⁺、Cl⁻和尿素浓度分别为211.9、207.8和195.9 mmol L⁻¹。将淡水D. sabina暴露于100%的海水中8天，与留在淡水中的对照动物相比，它们的血细胞比容没有显著变化。然而，血浆渗透压显著增加（953 mOsm kg⁻¹），血浆中Na⁺、Cl⁻和尿素浓度分别显著增加至319.13、296.1和329.76 mmol L⁻¹。适应海水的D. sabina的血浆相对于100%的海水是低渗和低离子的。淡水D. sabina的直肠腺重量与体重（RGBW）之比比报道的海洋D. sabina的RGBW之比低约80%；适应海水后，RGBW之比没有显著增加。这可能表明鳃和肾脏机制也参与离子排泄。我们得出结论，淡水D. sabina在生理上是广盐性的，尚未进化出狭盐性淡水Potamotrygonid黄貂鱼的渗透调节策略。
