(A) Mean gill burst frequency during last 3 min of normoxia in control and nicotine- or ethanol-exposed early and late metamorphic tadpoles. The gill burst frequency of early and late metamorphic nicotine-exposed tadpoles were both less than controls (* = P ≤ 0.05). Late metamorphic nicotine-exposed tadpoles had a lower gill burst frequency than early metamorphic nicotine-exposed tadpoles (+ = P = 0.01). Mean lung burst frequency during last 3 min of normoxia,10, 60, 90, 120, 150, and 180 min of hypoxia, and 30 min of normoxic recovery in control and nicotine- or ethanol-exposed early (B) and late metamorphic tadpoles (C). Early metamorphic ethanol-exposed tadpoles increased gill burst frequency from 90 –180 min of hypoxia (* = P ≤ 0.05). Late metamorphic control tadpoles increased gill burst frequency at 60 and 90 min of hypoxia (* = P ≤ 0.05). Late metamorphic nicotine-exposed tadpoles increased gill burst frequency at 90 and 120 min of hypoxia (* = P ≤ 0.05). Data presented are mean ± SE for 6 – 7 tadpoles.