Ammonia excretion by the gills of two marine teleost fish: The importance of NH4+ permeance

Abstract Varying the concentration of un‐ionized ammonia (NH 3 ) in the medium perfusing the gills of the isolated fish head while holding the total ammonia (NH 4 + + NH 3 ) concentration constant had no significant effect on gill ammonia excretion. In contrast, alteration in the medium NH 4 + concentration at a fixed NH 3 concentration produced a significant change in ammonia excretion. Thus, gill ammonia excretion was related to medium NH 4 + , not NH 3 , concentration.