All anabantoid species with a labyrinth organ are continuous air-breathing fish in both normoxic and hypoxic environments, although not all anabantoid species have apparent morphological modifications between the anterior and posterior gills as seen in T. leeri (Huang et al., 2008) and T. microlepis (Huang et al., 2010). For other anabantoid fish species that have no morphological modification in the gills, documenting their physiological responses to environmental stresses is important from a comparative point of view. Thus, for comparative purposes we chose T. lalius, as this species has no apparent differences among its gills.