Gills and air-breathing organ in O2 uptake, CO2 excretion, N-waste excretion, and ionoregulation in small and large pirarucu (Arapaima gigas)

In the pirarucu (Arapaima gigas), gill surface area and thus gas exchange capacity of the gills are reduced with proceeding development. It, therefore, is expected that A. gigas, starting as a water breather, progressively turns into an obligate air-breathing fish using an air-breathing organ (ABO) for gas exchange. We assessed the air-breathing activity, O2 and CO2 exchange into air and water, ammonia-N and urea-N excretion, ion flux rates, and...