Hypoxia-induced developmental plasticity of the gills and air-breathing organ of Trichopodus trichopterus

The air‐breathing blue gourami Trichopodus trichopterus, an anabantid with a suprabranchial labyrinth organ, was used to study morphological development of respiratory systems in response to chronic hypoxia (13% O2, combined aquatic and aerial hypoxia). Overall growth (fork length, wet mass and cutaneous surface area) of T. trichopterus did not differ between control fish and those reared in hypoxia. Both lamellar and labyrinth surface areas of the hypoxic larvae, however, increased more rapidly than controls, producing c. 16% larger lamellar and 30% larger labyrinth mass‐specific surface areas within the first 120 days of development. This is the first study to show developmental respiratory plasticity of a bimodally respiring fish. It reveals that chronic hypoxia stimulates development of the gills and air‐breathing organ, and that labyrinth growth is even more sensitive to hypoxia than branchial growth.