Nitrogen metabolism and excretion in fish: integration from behaviour to genes

所有动物在消化食物或维持体内蛋白质的正常过程中都会产生氨形式的废氮。氨对神经系统是有毒的，并且在人类中血液氨水平的两倍（例如，如在肝脏或肾脏疾病中所见）最终可导致昏迷和死亡。因此，所有动物必须要么直接排泄氨（水生动物可能将氨排泄到水中），要么将其解毒为毒性较小的化合物，以便以更浓缩的形式排泄（例如，尿素，如在许多陆生动物中，包括人类）。人们曾经认为，在鱼类等水生物种中产生尿素的基因没有表达，因为它们在直接排泄氨占主导地位的水生环境中不需要。然而，近几十年来的研究表明，这些基因实际上是（可能是大多数）胚胎鱼所需要的，而且也很少被某些鱼类作为成年鱼使用。拟议的研究检查了一个这样的家庭的鱼，蟾鱼和海军军官候补生，其中包含选定的成员，使和排泄尿素作为含氮废物。该小组将被用于研究一种新的假设，即尿素是用来“掩盖”蟾蜍鱼的气味，以潜在的捕食者。在胃肠道，鳃和神经系统，使蟾鱼控制尿素排泄离散脉冲的精确机制将被检查。此外，还将研究涉及尿素和氨的运输和代谢的几个关键基因的作用，包括所谓的恒河猴蛋白（在人类中负责输血中重要的“Rh因子”）。这项研究最终可能会应用于鱼类养殖。

All animals produce waste nitrogen as ammonia when they digest a meal, or in the normal maintenance of body protein. Ammonia is toxic to the nervous system, and as little as a doubling of blood ammonia levels in humans (e.g., as might be seen in liver or kidney disease) can eventually lead to coma and death. Therefore, all animals must either excrete ammonia directly (to the water as is possible in aquatic animals) or detoxify it to a less toxic compound for excretion in a more concentrated form (e.g., urea, as in many terrestrial animals, including humans). It was once thought that the genes for urea production in aquatic species like fish were not expressed because they were not needed in an aquatic environment where direct excretion of ammonia predominates. However, research in recent decades has shown that these genes are in fact needed in (probably most) embryonic fish, and are also used rarely by some species of fish as adults. The proposed research examines one such family of fishes, the toadfish and midshipmen, that contains selected members that make and excrete urea as a nitrogenous waste product. The group will be used to study a novel hypothesis that urea is use to 'cloak' the scent of toadfish to potential predators. The precise mechanisms in the gastrointestinal tract, gills and nervous system that allow toadfish to control urea excretion in discrete pulses will be examined. Furthermore, the action of several key genes involved in transport and metabolism of urea and ammonia will be studied, including the so-called Rhesus proteins (which in humans are responsible for the "Rh factors" important in blood transfusions). The research may eventually have application in fish aquaculture.