THE INFLUENCE OF CARBON DIOXIDE ON THE TOXICITY OF UN-IONIZED AMMONIA TO RAINBOW TROUT (SALMO GAIRDNERII RICHARDSON)

The toxicity of solutions of ammonia to fish in different dilution waters showed a variation which was not entirely related to the concentration of the un-ionized ammonia molecule. Evidence is presented which shows that this variation can be attributed to the increase in the concentration of free carbon dioxide at the gill surface, which causes a decrease in both the pH value and the concentration of unionized ammonia present; the extent of the decrease depends on the initial concentration of free carbon dioxide in the bulk of the solution. Quantitative measurements of the relation between the free carbon dioxide concentration of the water and the toxicity of un-ionized ammonia are correlated with a theoretical estimation of the pH value of the water at the gill surface.