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Ammonia and Acid-Base Balance During High Ammonia Exposure in a Marine Teleost (Myoxocephalus Octodecimspinosus)
1 The Mount Desert Island Biological Laboratory Salsbury Cove, ME 04672, USA; Department of Biology, Georgia Southern College Statesboro, GA 30460, USA
2 The Mount Desert Island Biological Laboratory Salsbury Cove, ME 04672, USA; Department of Zoology, University of Florida Gainesville, FL 32611, USA
For the first time in a marine teleost (the long-horned sculpin; Myoxocephalus octodecimspinosus), the maintenance of blood pH, PCoCo2, [HCO3- and the net movements of NH4+ HCO3- and H+ between the fish and the water have been studied during exposure to ammonia stress induced either by infusion (NH4Cl or NH4HCO3; 5 mmol kg-1) or by external application (NH4Cl; approx. 1 mmoll-1).
Following NH4Cl infusion, a rapid decrease in blood pH (0.36 units) and [HCO3-] (2.38 mmoll-1) was observed, and within 1 h about 40% of the ammonia load had been excreted to the water. Analysis of NH4+ and HCO3- transfers revealed that the total ammonia (TAmm) efflux was due to a loss of NH3 and NH4+ in approximately equal proportions when an outwardly directed NH3 diffusion gradient was established.
Infusion of NH4HCO3 induced only small changes in plasma pH, and the rate of net HCO3- excretion was some 90% higher than that of NH4+ over 20 h. These data indicate a predominance of NH3 as the form of ammonia lost. In both infusion experiments, a presumed intracellular buffering of a majority of the ammonia load was noted.
High external TAmm induced an initial uptake of NH4+, but after 4 h of exposure ammonia efflux resumed even though NH3 diffusion gradients were negligible. Thus, in this seawater teleost, a role for the excretion of ammonia in the form of NH4+ is also likely.
Key words: marine teleost, ammonia, acid-base, gill, ion transfer
Accepted on May 3, 1988
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