The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

• Published in: Physiological reviews Vol. 85; no. 1; pp. 97 - 177
• Main Authors: Evans, David H, Piermarini, Peter M, Choe, Keith P
• Format: Journal Article
• Language: English
• Published: United States Am Physiological Soc 01.01.2005; American Physiological Society
• Subjects: Acid-Base Equilibrium - physiology; Acids; Animals; Excretory system; Fish; Fishes - physiology; Gills; Gills - physiology; Gills - ultrastructure; Nitrogen; Nitrogen Compounds - metabolism; Oxygen - metabolism; Physiological aspects; Water-Electrolyte Balance - physiology
• ISSN: 0031-9333; 1522-1210
• DOI: 10.1152/physrev.00050.2003

Department of Zoology, University of Florida, Gainesville, Florida; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and Mt. Desert Island Biological Laboratory, Salisbury Cove, Maine The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain. 1 The use of heterologous antibody and the fact that sequence for ENaC does not exist in the zebrafish or fugu genomes do not allow for a definitive conclusion that the gill Na + channel is ENaC; hence, it will be designated ENaC-like in this review. 2 We are indebted to Dr. L. B. Kirschner, who brought these quotes to our attention. 3 This model assumes that the transepithelial potential (TEP) across the marine teleost gills is of the order of +25 mV (plasma relative to SW) so that Na + is in electrochemical equilibrium. Measurement of a gills-only TEP in vivo has not been reported, but 50% of the published whole body TEPs (salt bridge in peritoneal fluids versus salt bridge in SW) are <20 mV, including six species that have an inside-negative TEP (177, 622). Thus it is not clear if the model for NaCl extrusion in Figure 29 is applicable to all marine teleosts. 4 In addition, gill vessels may respond to hypoxia directly as has been described for the efferent branchial artery and other vessels in the trout (704) as well as various systemic vessels from agnathan species (562). 5 It has been suggested that the emerging roles for both STC and UII in mammalian physiology and pathophysiology are good examples of the "singular contributions of fish neuroendocrinology to mammalian regulatory peptide research" (119).