Regulation of Ureotely in Batrachoidid Fishes

University Of Miami, Coral Gables FL

Investigators

Abstract

Regulation of Ureotely in Batrachoidid Fishes Patrick J. Walsh, M. Danielle McDonald University of Miami Until recently, it has been commonly accepted knowledge that fish and other aquatic species excrete ammonia as their main waste product following a meal. Ammonia is ultimately toxic, primarily to the brain, so fish and other aquatic species rid their bodies of ammonia as soon as it is produced, and its harmful effects are immediately diluted by the "infinite" volume of the surrounding water. However, when animals evolved to live on land, and did not have the diluting effects of a surrounding water environment, they needed to adopt alternate means of ridding their bodies of this toxin. So, terrestrial animals make (from ammonia) and excrete alternative waste products (urea and uric acid), which they can store in their bodies at higher concentrations without harmful effect until they are able to consume enough water with which to excrete them in their urine; the process of making and excreting urea is known as "ureotely". Surprisingly, in recent years, Walsh and colleagues have discovered that a common marine fish living in the bays and estuaries of the Southeastern US, the gulf toadfish (Opsanus beta), is an exception to this rule, opting to excrete urea instead of ammonia under certain stressful circumstances. Even more unusual, the toadfish excretes all of its urea in a single pulse lasting only a few hours across the gills. Thus the goals of this research project are to understand how this fish species is able to make and excrete urea, and to understand the ecological and evolutionary reasons for why it does so, and why it pulses its urea excretion. The ability to make urea requires a great deal of energy, which would otherwise be spent on predator avoidance, reproduction, etc., so it is reasonable to assume that the ability to make and excrete urea is somehow favored by natural selection, and contributes to the fish's ability to survive stressful conditions and propagate. These goals will be approached with several different methods. In one portion of the study biochemical and molecular biology techniques will be used to understand how the fish shifts from making ammonia to making urea during stress, focusing on enzymes of urea production in the liver. In a second part of the study, physiological studies on how urea is excreted at the gill will be performed. In the third part of the study, field experiments will be used to test the hypotheses that urea production is important to the survival of the fish because the fish lives in an environment with high ammonia concentration, and/or that the pulses of urea excretion help it to be better at chemically camouflaging itself from predators. Lastly, studies will be conducted at the level of DNA to see how closely related species are within this family of fishes, and then compare members of the family that either do or do not adopt this mode of coping with stress. Through these "family tree" studies the PIs intend to determine where in the evolution of these species this trait has appeared or not, giving additional clues as to why the toadfish makes and excretes urea. The overall broader importance of the research is that it will help to understand how rapidly aquatic organisms are able to adapt to changing stressful environments on both an individual and generational time scale, and this work may eventually serve as a case study in the evolution of a complex physiological trait. This type of information becomes more and more valuable as our environment changes due to human influence. Furthermore, since ammonia is one of the most important waste byproducts in aquaculture that must be removed by expensive means to keep fish healthy, these studies may potentially suggest more efficient ways to culture fish and other aquatic species. This research will take place with significant international collaboration (with scientists from 5 other countries). Furthermore, since the University of Miami is a Minority Serving Institution, the PI will be able to recruit student researchers from minorities/underrepresented groups.