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Mechanism of acidification of expired water in fish

University of British Columbia

The effect of varying inhaled water pH on the acidification or alkalization of water as it passes over the gills in rainbow trout (Salmo gairdneri) was investigated by exposing the fish to pH 9.91 and pH 3.88 water. In the control and high pH treatment, water was acidified as it flowed over the gills of the fish because of the dominant effect of CO₂ hydration. Water was alkalized as it flowed over the gills of the fish in the low pH treatment due to NH₄⁺ formation and perhaps HCO₃₋ dehydration. The overall result of CO₂ and NH₃ excretion is to ameliorate the change of expired water pH in the face of changes in pH of inspired water. Carbon dioxide excretion was not significantly affected by the high or low pH treatments but ammonia was accumulated in fish plasma in both cases. The impact of Na⁺/H⁺ (NH₄⁺) and Cl⁻/HCO₃₋ exchange processes on the acidification or alkalization of expired water has also been examined. Amiloride or SITS was introduced to the water to inhibit the ionic exchange processes and environmental water pH was gradually lowered from neutral to acidic. Under acidic conditions, molecular CO₂ and NH₃ excretion alone could account for all the proton concentration changes from inspired to expired water, indicating that Na⁺/H⁺(NH₄⁺) transport was inhibited by low environmental pH. In neutral environments, the proton concentration changes were the result of molecular CCh and NH3 excretion, and sodium influx in exchange for H⁺(NH₄⁺). Cl⁻/HCO₃₋ exchange was not an important pathway for carbon dioxide elimination but inhibition of Na⁺/H⁺(NH₄⁺) exchange caused a reduction of ammonia excretion.

Text

2010-08-21

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http://hdl.handle.net/2429/27585

Zoology

University of British Columbia

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