CRUI: Osmoregulation in Euryhaline Fish: Physiology, Ecology and Molecular Biology.

大多数鱼类完全局限于淡水（FW）或海水（SW），不能在其他环境中生活或适应。令人惊讶的是，所有硬骨鱼类血液中的内部盐和有机分子（溶质）都保持在一个“中间”浓度（这实际上与哺乳动物相似）。换句话说，咸水中的鱼可能会受到压力，因为它们生活在比血液含盐量高3倍的环境中，因此必须“泵出”摄入的额外盐分。这需要分子运输蛋白（如钠/钾泵和其他离子泵和通道）。另一方面，FW鱼面临着“浸水”的问题。换句话说，组织和血液中较高浓度的盐会导致鱼类通过扩散（也称为渗透）获得水分。这些鱼必须排出多余的水分，保存盐分。它们通过分子运输蛋白来实现这一点。一般来说，体内盐和水平衡的控制（渗透调节）需要大量的代谢能量来驱动。大多数人都知道，像鲑鱼和鳗鱼这样的少数鱼类在FW和SW度过了它们一生的一部分。这些鱼实际上是从FW代谢转换到SW代谢，这一过程可能会产生代谢压力。一种令人惊讶的小鱼（3英寸长），鳉鱼（Fundulus heteroclitus），已被证明具有非凡的渗透调节能力。这种鱼可以无限期地在淡水或淡水中生存，其浓度是海水的3倍。此外，鳉鱼可能每天从西南洄游到西南，然后返回觅食（并在春天繁殖和产卵），这使它们看起来非常擅长渗透调节。目前，人们对代谢机制，特别是与之相关的分子转运蛋白有着浓厚的兴趣。事实上，在鳉鱼中发现的许多相同类型的蛋白质及其对盐度变化的反应也在鲑鱼和鳗鱼中发现。然而，对于鳉鱼（也许还有其他鱼类），人们提出了另一种机制来应对盐度压力，称为行为渗透调节。这个假设的核心是，在所有其他条件相同的情况下，鳉鱼会试图游向FW流，直到它们体内的盐和水的成分与外部水的成分相似（大约1/3的强度SW），并留在那里保存代谢能量，否则这些能量将被消耗在将盐吸入或排出鱼体内。初步数据支持这样的假设，即鳉鱼可能会寻找约为西南三分之一的盐度。这一新观点在生理学和生态学上都具有广泛的意义。主要研究人员将测量鳉鱼的渗透调节代谢能量需求。利用基于DNA的技术，他们将测量鳉鱼分子运输蛋白的存在和变化。他们还将调查野生鳉鱼的生态，并试图将自然分布和繁殖行为与预测的盐度偏好联系起来。该项目的一个非常重要的部分是，首席研究员每年将带领一个由8名本科生组成的团队（每4年一次），他们将在学年期间在他们的家乡机构进行这项研究，然后在夏季来到Mount Desert Island生物实验室进行2个月的实地考察，生理学和分子生物学。学生们将有机会在国内最好的海洋实验室之一进行原创性研究，同时学习许多领域的现代技术。希望这段经历能让这些学生感受到对科学研究的热情和成就感，这将激励他们在未来的职业生涯中。

Most fish are confined entirely to fresh water (FW) or seawater (SW) and cannot live in or adapt to the other environment. What may be surprising is that the internal salts and organic molecules (solutes) in the blood of all bony fishes are maintained in an "intermediate" concentration (which is actually similar to that in mammals). In other words, fish in salt water may suffer stress because they are living in a medium about 3 times as salty as their blood and therefore must "pump out" extra salt that is ingested. This requires molecular transport proteins (such as the sodium/potassium pump and other ion pumps and channels). FW fish, on the other hand, face the problem of becoming "waterlogged". In other words, the higher concentrations of salts in their tissues and blood cause the fish to gain water by diffusion (also called osmosis). These fish must rid themselves of the extra water and conserve salts. They do this by using molecular transport proteins. In general the control of internal salt and water balance (osmoregulation) requires significant metabolic energy to power it. As most people know, a small number of fish like salmon and eels spend a part of their life in FW and part of their life in SW. These fish literally switchover from the FW metabolism to the SW metabolism, a process that may be metabolically stressful. A surprising little fish (3 inches long), the killifish (Fundulus heteroclitus), has been shown to have phenomenal osmoregulatory abilities. This fish can survive indefinitely in FW or in SW up to 3 times more concentrated than ocean water. Furthermore, killifish may migrate daily from SW to FW and back to feed (and to breed and lay eggs in the Spring) making them appear to be unusually adept at osmoregulation. At present there is intense interest in the metabolic machinery and especially the molecular transport proteins that are involved. Indeed, many of the same types of proteins and their responses to salinity change that are found in killifish also are found in salmon and eels. However, with killifish (and perhaps other fish as well) another mechanism, to deal with salinity stress has been suggested, termed behavioral osmoregulation. The heart of this hypothesis is that, all other things being equal, killifish will try to swim up FW streams to the point where their internal salt and water composition resembles that of the external water (about 1/3 strength SW) and stay there conserving metabolic energy that would otherwise be expended pumping salts in or out of the fish. Preliminary data support the hypothesis that killifish may seek salinities about 1/3 that of SW. This new idea has broad implications physiologically and ecologically. The principal investigators will measure the metabolic energy requirements for osmoregulation in killifish. Using DNA based techniques, they will measure the presence of and changes in the molecular transport proteins in killifish. They also will investigate the ecology of wild killifish and attempt to correlate natural distributions and breeding behavior with projected salinity preferences. A very important part of this project is that the principal investigators will lead a team of 8 undergraduate students per year (for each of 4 years) who will work during their academic year on this research at their home institutions and then come to Mount Desert Island Biological Laboratory for 2 months during the summer to do fieldwork, physiology and molecular biology. The students will have the opportunity to do original research while learning modern techniques in many fields at one of the country's finest marine laboratories. It is expected that this experience show these students the passion and fulfillment of scientific research that will motivate them in their future careers.