Comparative Biochemistry and Physiology, Part A 146 (2007) S87–S96www.elsevier.com/locate/cbpa

Society for Experimental Biology Annual Main Meeting31st March – 4th April 2007, Glasgow, Scotland

A3–DRINKING, SALT AND OSMOREGULATION

A3.1Control 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 arelatively constant level and independent of the medium theyinhabit. Body fluids of freshwater fish tend to be diluted byosmotic gain of water via the body surface and diffusive loss ofsalts via the body surface, gills and kidney. When dilutionreaches a threshold level, compensation is achieved byactivation of salt acquisition mechanisms in the gill epithelialcells such that an appropriate amount of salt is absorbed withappropriate water loss via the kidney. Substantial feeding mayresult in intake of excessive ions requiring a decrease in brachialabsorption of ions and activation of branchial ionic excretorymechanisms. Body fluids of marine fish tend to dehydratethrough osmotic loss of water and diffusive gain of ions via thehyperosmotic medium. When dehydration reaches a thresholdpoint, compensation is achieved by activation of drinking,intake of an appropriate quantity of sea water, absorption of thesea water in the gut and excretion of the appropriate amount ofsalts via the branchial epithelium and the gut. Whilst theprocesses of salt absorption and salt excretion in fish have beenexplored in some detail, there is as yet little understanding ofhow the individual processes are regulated and how integrationis achieved. This paper explores some recent ideas in the controlof body fluid composition in fish.

doi:10.1016/j.cbpa.2007.01.119

A3.2Osmoregulation in elasmobranch fish — A review

N.Hazon,AWells, (University of St.Andrews,UnitedKingdom);G. Anderson, (University of Manitoba, Canada); J. Good,R. Pillans, C. Franklin, (University of Queensland, Australia)

doi:10.1016/j.cbpa.2007.01.118

In recent years our understanding of the control of ion and ureametabolism in elasmobranch fish has increased with many morespecies being investigated. This has demonstrated that somespecies regarded previously as stenohaline marine are, at leastpartially, euryhaline and may survive in environments lessconcentrated than full seawater. In elasmobranch fish thesuccess of the osmotic strategy depends on retaining largeconcentrations of plasma urea in addition to relatively high, incomparison to most other vertebrates, plasma concentrations ofsodium and chloride. The strategy therefore depends on theintegrated control of hepatic urea production and branchial andrenal urea excretion and also on a balance of salt input at thegills and gut with salt output at the gills, kidney and via theunique elasmobranch rectal gland. This integrated response is,at least in part, controlled by a series of osmoregulatoryhormones and their possible role in the control of osmoregu-latory organs will be discussed. In this presentation recentfindings will be reviewed and the osmoregulatory strategies of apartially euryhaline species, Scyliorhinus canicula, with a fullyeuryhaline migratory species, Carcharhinus leucas, will becompared. This will allow new models for the control of ion andurea metabolism in elasmobranchs to be proposed for futureresearch.

doi:10.1016/j.cbpa.2007.01.120

A3.3Making a living out of drinking

J. Fuentes, (CCMar, CIMAR Laboratorio Associado, Portugal)

Water metabolism is of vital importance for most vertebratesincluding fish. The mechanisms regulating water ingestion(drinking) seem to vary in the degree of complication betweenterrestrial and aquatic vertebrates. Common to most species isthe dipsogenic action of the renin angiotensin system (RAS).