Publication Information

Basic Information

Access and Citation

AI Researcher Chatbot

Get quick answers to your questions about the article from our AI researcher chatbot

Primary Location

Authors

Topics

Keywords

Related Works

Title: $Branchial Sodium Exchange and Ammonia Excretion in the Goldfish <i>Carassius Auratus</i>. Effects of Ammonia-Loading and Temperature Changes
Abstract: ABSTRACT Krogh (1939) first suggested that in freshwater animals branchial or cutaneous excretion of ammonia may be related to sodium absorption. In both freshwater Crustacea (Astacus pallipes) and teleosts (Carassius auratus) independent active transport of Na+ and Cl− from the outside medium have been definitely established (Shaw, 1960a–c; Garcia Romeu &amp; Maetz, 1964). Sodium in particular may be absorbed at very high rates without an accompanying anion. The maintenance of the electroneutrality of the external and internal media necessitates an exchange with an endogenous ion during sodium movement. The possibility that ammonium ions may fulfil this role is suggested by the fact that the gill is the main site of ammonia excretion (Smith, 1929,1953) and indirect experimental evidence has supported this hypothesis. Addition of ammonia to the outside medium, a procedure which inhibits ammonia excretion, interferes with the sodium uptake (Shaw, 1960a; Maetz &amp; Garcia Romeu, 1964). Injection of ammonium ions, a procedure which increases ammonia excretion by the gill, produces an increase of sodium uptake in the goldfish (Maetz &amp; Garcia Romeu, 1964) and in the eel (Garcia Romeu &amp; Motais, 1966). No stoichiometric relationship between ammonia excretion rate and sodium net uptake in relation to experimental external salinity changes is, however, observed in the crayfish (Shaw, 1960b). Thus the exchange cannot be obligatory. In particular when ammonia excretion falls short of sodium uptake, a second exchange process, Na+ against H+, is thought to be operative, or when sodium uptake is blocked at low external sodium concentration, ammonium is thought to be accompanied by endogenous bicarbonate ions excreted by the gill (Shaw, 1960b).