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Control of salt and water balance in fish
Comparative Biochemistry and Physiology, Part A 146 (2007) S87 – S96 www.elsevier.com/locate/cbpa
Society for Experimental Biology Annual Main Meeting 31st March – 4th April 2007, Glasgow, Scotland
A3–DRINKING, SALT AND OSMOREGULATION A3.1 Control of salt and water balance in fish F. Eddy, (University of Dundee, United Kingdom) The concentration of the body fluid of fish is maintained at a relatively constant level and independent of the medium they inhabit. Body fluids of freshwater fish tend to be diluted by osmotic gain of water via the body surface and diffusive loss of salts via the body surface, gills and kidney. When dilution reaches a threshold level, compensation is achieved by activation of salt acquisition mechanisms in the gill epithelial cells such that an appropriate amount of salt is absorbed with appropriate water loss via the kidney. Substantial feeding may result in intake of excessive ions requiring a decrease in brachial absorption of ions and activation of branchial ionic excretory mechanisms. Body fluids of marine fish tend to dehydrate through osmotic loss of water and diffusive gain of ions via the hyperosmotic medium. When dehydration reaches a threshold point, compensation is achieved by activation of drinking, intake of an appropriate quantity of sea water, absorption of the sea water in the gut and excretion of the appropriate amount of salts via the branchial epithelium and the gut. Whilst the processes of salt absorption and salt excretion in fish have been explored in some detail, there is as yet little understanding of how the individual processes are regulated and how integration is achieved. This paper explores some recent ideas in the control of body fluid composition in fish. doi:10.1016/j.cbpa.2007.01.119
In recent years our understanding of the control of ion and urea metabolism in elasmobranch fish has increased with many more species being investigated. This has demonstrated that some species regarded previously as stenohaline marine are, at least partially, euryhaline and may survive in environments less concentrated than full seawater. In elasmobranch fish the success of the osmotic strategy depends on retaining large concentrations of plasma urea in addition to relatively high, in comparison to most other vertebrates, plasma concentrations of sodium and chloride. The strategy therefore depends on the integrated control of hepatic urea production and branchial and renal urea excretion and also on a balance of salt input at the gills and gut with salt output at the gills, kidney and via the unique elasmobranch rectal gland. This integrated response is, at least in part, controlled by a series of osmoregulatory hormones and their possible role in the control of osmoregulatory organs will be discussed. In this presentation recent findings will be reviewed and the osmoregulatory strategies of a partially euryhaline species, Scyliorhinus canicula, with a fully euryhaline migratory species, Carcharhinus leucas, will be compared. This will allow new models for the control of ion and urea metabolism in elasmobranchs to be proposed for future research. doi:10.1016/j.cbpa.2007.01.120
A3.3 Making a living out of drinking J. Fuentes, (CCMar, CIMAR Laboratorio Associado, Portugal)
A3.2 Osmoregulation in elasmobranch fish — A review N. Hazon, AWells, (University of St. Andrews, United Kingdom); G. Anderson, (University of Manitoba, Canada); J. Good, R. Pillans, C. Franklin, (University of Queensland, Australia) doi:10.1016/j.cbpa.2007.01.118
Water metabolism is of vital importance for most vertebrates including fish. The mechanisms regulating water ingestion (drinking) seem to vary in the degree of complication between terrestrial and aquatic vertebrates. Common to most species is the dipsogenic action of the renin angiotensin system (RAS).
Society for Experimental Biology Annual Main Meeting 31st March – 4th April 2007, Glasgow, Scotland
A3–DRINKING, SALT AND OSMOREGULATION A3.1 Control of salt and water balance in fish F. Eddy, (University of Dundee, United Kingdom) The concentration of the body fluid of fish is maintained at a relatively constant level and independent of the medium they inhabit. Body fluids of freshwater fish tend to be diluted by osmotic gain of water via the body surface and diffusive loss of salts via the body surface, gills and kidney. When dilution reaches a threshold level, compensation is achieved by activation of salt acquisition mechanisms in the gill epithelial cells such that an appropriate amount of salt is absorbed with appropriate water loss via the kidney. Substantial feeding may result in intake of excessive ions requiring a decrease in brachial absorption of ions and activation of branchial ionic excretory mechanisms. Body fluids of marine fish tend to dehydrate through osmotic loss of water and diffusive gain of ions via the hyperosmotic medium. When dehydration reaches a threshold point, compensation is achieved by activation of drinking, intake of an appropriate quantity of sea water, absorption of the sea water in the gut and excretion of the appropriate amount of salts via the branchial epithelium and the gut. Whilst the processes of salt absorption and salt excretion in fish have been explored in some detail, there is as yet little understanding of how the individual processes are regulated and how integration is achieved. This paper explores some recent ideas in the control of body fluid composition in fish. doi:10.1016/j.cbpa.2007.01.119
In recent years our understanding of the control of ion and urea metabolism in elasmobranch fish has increased with many more species being investigated. This has demonstrated that some species regarded previously as stenohaline marine are, at least partially, euryhaline and may survive in environments less concentrated than full seawater. In elasmobranch fish the success of the osmotic strategy depends on retaining large concentrations of plasma urea in addition to relatively high, in comparison to most other vertebrates, plasma concentrations of sodium and chloride. The strategy therefore depends on the integrated control of hepatic urea production and branchial and renal urea excretion and also on a balance of salt input at the gills and gut with salt output at the gills, kidney and via the unique elasmobranch rectal gland. This integrated response is, at least in part, controlled by a series of osmoregulatory hormones and their possible role in the control of osmoregulatory organs will be discussed. In this presentation recent findings will be reviewed and the osmoregulatory strategies of a partially euryhaline species, Scyliorhinus canicula, with a fully euryhaline migratory species, Carcharhinus leucas, will be compared. This will allow new models for the control of ion and urea metabolism in elasmobranchs to be proposed for future research. doi:10.1016/j.cbpa.2007.01.120
A3.3 Making a living out of drinking J. Fuentes, (CCMar, CIMAR Laboratorio Associado, Portugal)
A3.2 Osmoregulation in elasmobranch fish — A review N. Hazon, AWells, (University of St. Andrews, United Kingdom); G. Anderson, (University of Manitoba, Canada); J. Good, R. Pillans, C. Franklin, (University of Queensland, Australia) doi:10.1016/j.cbpa.2007.01.118
Water metabolism is of vital importance for most vertebrates including fish. The mechanisms regulating water ingestion (drinking) seem to vary in the degree of complication between terrestrial and aquatic vertebrates. Common to most species is the dipsogenic action of the renin angiotensin system (RAS).