Pillans Richard D, Good Jonathan P, Anderson W Gary, Hazon Neil, Franklin Craig E
School of Life Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia.
J Comp Physiol B. 2005 Jan;175(1):37-44. doi: 10.1007/s00360-004-0460-2. Epub 2004 Nov 24.
This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater (SW). Juvenile C. leucas captured in FW (3 mOsm l(-1) kg(-1)) were acclimated to SW (980-1,000 mOsm l(-1) kg(-1)) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l(-1) kg(-1). In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l(-1) kg(-1)) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na(+), Cl(-), K(+), Mg(2+), Ca(2+), urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na(+)/K(+)-ATPase activity. Na(+)/K(+)-ATPase activity in the gills and intestine was less than 1 mmol Pi mg(-1) protein h(-1) and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na(+)/K(+)-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na(+)/K(+)-ATPase activity was 5.6+/-0.8 and 9.2+/-0.6 mmol Pi mg(-1) protein h(-1), respectively. Na(+)/K(+)-ATPase activity in the kidney of FW and SW acclimated animals was 8.4+/-1.1 and 3.3+/-1.1 Pi mg(-1) protein h(-1), respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.
本研究考察了广盐性板鳃亚纲动物白真鲨在适应淡水（FW）和海水（SW）环境下的渗透调节状态。捕获于淡水（3毫渗摩尔/升·千克）的幼年白真鲨在16天内适应了海水（980 - 1000毫渗摩尔/升·千克）环境。一个淡水组在相似时间段内圈养。在淡水中，公牛鲨是高渗调节者，血浆渗透压为595毫渗摩尔/升·千克。在海水中，公牛鲨的血浆渗透压（940毫渗摩尔/升·千克）显著高于适应淡水的动物，且相对于环境略呈低渗状态。适应海水的公牛鲨血浆中Na⁺、Cl⁻、K⁺、Mg²⁺、Ca²⁺、尿素和氧化三甲胺（TMAO）浓度均显著更高，其中尿素和TMAO的增加最为显著。从适应淡水和海水的动物身上获取鳃、直肠腺、肾脏和肠道组织，分析其最大Na⁺/K⁺ - ATP酶活性。鳃和肠道中的Na⁺/K⁺ - ATP酶活性低于1毫摩尔无机磷/毫克蛋白质·小时，适应淡水和海水的动物之间活性无差异。相比之下，直肠腺和肾脏中的Na⁺/K⁺ - ATP酶活性显著高于鳃和肠道，且适应淡水和海水的组之间存在显著差异。在淡水和海水中，直肠腺的Na⁺/K⁺ - ATP酶活性分别为5.6±0.8和9.2±0.6毫摩尔无机磷/毫克蛋白质·小时。适应淡水和海水的动物肾脏中的Na⁺/K⁺ - ATP酶活性分别为8.4±1.1和3.3±1.1无机磷/毫克蛋白质·小时。因此，幼年公牛鲨具有适应海水的渗透调节可塑性；它们偏好盐度低的河流上游，因此可能是为了躲避捕食者和/或增加食物丰富度，而非由于生理限制。
