Regulation of Ureotely in Batrachoidid Fishes

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Until recently, it has commonly been accepted knowledge that fish and other aquatic species excrete ammonia as the 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" sink 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 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. However, in recent years, the PIs have discovered that a common fish in the Southeastern US, the gulf toadfish (Opsanus beta) is an exception to this rule, excreting urea instead of ammonia under certain stressful circumstances. 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. The ability to make urea and uric acid 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 selectively advantageous, and contributes to the fish's ability to survive and propagate.The investigators will take three approaches to understanding the mechanisms and significance of urea excretion in fish. One portion of the study will employ biochemical and molecular biology techniques to understand how the fish shifts from making ammonia to making urea, focusing on enzymes of the liver. A second part of the study will focus on physiological studies of how urea is excreted at the gill. A third part of the study, will focus on field experiments that 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 urea excretion helps the fish to be better at chemically camouflaging itself from predators. This research will elucidate how rapidly aquatic organisms are able to adapt to changing environments on both an individual and an evolutionary time scale. This type of information becomes more and more valuable as our environment changes due to man's influence. Furthermore, since ammonia is one of the most important byproducts in aquaculture that must be removed, results of these studies may have implications for fish production.