Gill morphometric and gill plasticity of the air-breathing striped catfish (Pangasianodon hypophthalmus) exposed to different temperatures (present day 27°C and future 33°C) and different air saturation levels (92% and 35%) during 6 weeks were investigated using vertical sections to estimate the respiratory lamellae surface areas, harmonic mean barrier thicknesses, and gill component volumes. Gill respiratory surface area (SA) and harmonic mean water - blood barrier thicknesses (HM) of the fish were strongly affected by both environmental temperature and oxygen level. Thus initial values for 27°C normoxic fish (12.4 ± 0.8 g) were 211.8 ± 21.6 mm² g⁻¹ and 1.67 ± 0.12 μm for SA and HM respectively. After 5 weeks in same conditions or in the combinations of 33°C and/or PO₂ of 55 mmHg, this initial surface area scaled allometrically with size for the 33°C hypoxic group,whereas branchial SAwas almost eliminated in the 27°C normoxic group, with other groups intermediate. In addition, elevated temperature had an astounding effect on growthwith the 33°C group growing nearly 8-fold faster than the 27°C fish.