Regulation and Function of Urea Synthesis in Teleost Fish

当动物进食、消化和吸收含蛋白质的食物时，以氨的形式产生氮原子作为废物。氨对中枢神经系统是一种非常强效的毒素，所以必须迅速从他们的身体中清除。在鱼类和其他水栖动物身上，周围的水实际上是无限吸收氨的水槽，所以氮废物被简单而迅速地以氨的形式转移到水中。然而，陆生动物没有浸泡在水中，需要节约用水，所以它们不能轻易地去除氨。它们将氨转化为尿素，由于尿素对中枢神经系统的毒性较小，因此可以以更高的浓度储存，然后以浓缩的尿液排出，从而节省水分。将氨转化为尿素会从其他身体功能（如生长、繁殖等）中转移能量，因此从进化的角度来看，制造尿素不是一项微不足道的投资。我们发现了一种更高级的硬骨鱼（硬骨）海鱼，海湾蟾蜍鱼，出人意料地产生和排泄尿素。这笔拨款将使我们能够研究这种现象发生的原因和方式，以及它的生态和进化意义。除了增强我们在这一生理过程领域的基本知识外，这些研究可能在某种程度上为水产养殖和环境管理的实际发展提供有用的信息。

When animals eat, digest and assimilate a protein-containing meal, nitrogen atoms in the form of ammonia are produced as waste. Ammonia is a very potent toxin to the central nervous system, so it must be rapidly removed from their bodies. In fish and other water-dwelling animals, the surrounding water is a virtually limitless sink for this ammonia, so nitrogen waste is simply and rapidly removed to the water as ammonia. Land-dwelling animals, however, not being immersed in water, have the need to conserve water, so they cannot readily remove ammonia as such. They transform ammonia to urea, which since it is less toxic to the central nervous system, can be stored in higher concentrations before being eliminated in a concentrated urine which conserves water. Transforming ammonia to urea diverts energy from other bodily functions (e.g., growth, reproduction, etc.), so in an evolutionary sense making urea is not a trivial investment. We have discovered a higher teleost (bony) marine fish, the gulf toadfish, that unexpectedly makes and excretes urea. This grant will allow us to study why and how this phenomenon occurs and its ecological and evolutionary significance. In addition to enhancing our basic knowledge in this area of physiology processes, these studies may at some point provide information useful to practical developments in aquaculture and environmental management.