Studies of Ammonia in the Rainbow Trout Physico-Chemical Parameters, Acid-Base Behaviour and Respiratory Clearance

  • Cameron J
  • Heisler N
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Abstract

Ammonia (NH3) is only slightly more soluble (+3·4%) in the plasma of rainbow trout than in water, and its pK′ is only 0·14 units higher than in fresh water at 15 °C. Determination of these physico-chemical parameters together with measurements of blood and water pH and total ammonia concentrations allowed calculation of the mean resting partial pressure gradient across the gills (54 × 10−s6Torr) and estimation of the gill permeability coefficient (D = 1·3 × 10−5cm−1).Under normal resting conditions of low external NH3 and pH, diffusive movement of NH3 appears to account adequately for ammonia excretion in the rainbow trout; 90 ± 10% of the excreted ammonia appears to originate from the blood, rather than from de novo synthesis of ammonia in the gills.During the high external ammonia treatments, the fish reached a steady state with a net inward ammonia gradient, which could be accounted for by a counter-balancing Na+/NH4+ exchange. Ammonium salt infusions or injections which stimulate Na+ influx are not sufficient demonstrations of Na+/NH4+ exchange, since acidosis is produced, and alternate interpretations of the Na+ flux stimulation are possible, such as enhanced Na+/H+ exchange.

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Cameron, J. N., & Heisler, N. (1983). Studies of Ammonia in the Rainbow Trout Physico-Chemical Parameters, Acid-Base Behaviour and Respiratory Clearance. Journal of Experimental Biology, 105(1), 107–125. https://doi.org/10.1242/jeb.105.1.107

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