An in vivo respirometer–metabolism chamber was used to obtain respiratory–cardiovascular physiology under normoxic and hypoxic conditions, and xenobiotic gill absorption (flux) data on adult lake trout ( Salvelinus namaycush) over a 48-h exposure period at 11±1°C. An oral membrane was used to separate inspired and expired water flows, providing the first direct measurements of chemical flux across the gills of lake trout. Overall mean values (±S.D.) for normoxic respiratory function were: ventilation rate (V R)=53±9 # min −1, ventilation volume (Q V)=7±2 l kg −1 h −1, respiratory stroke volume (SV R)=2±1 ml, oxygen consumption (VO 2)=39±8 mg kg −1 h −1, oxygen utilization (U)=53±14%, and effective respiratory volume (Q W)=4±1 l kg −1 h −1. The resting Q V, Q W, and VO 2 seen in these lake trout were lower than seen previously in other salmonids. No significant differences ( P≥0.05) in respiratory function were detected between males and females. Trout subjected to hypoxia (30% of saturation) showed no changes in U or VO 2, while V R decreased (42±6 # min −1), Q V increased (22±6 l kg −1 h −1) and SV R increased (8±3 ml). Cardiovascular and blood gas measurements determined under normoxic conditions were heart rate (H R)=73±8 # min −1, cardiac output (Q C)=15±2 ml kg −1 min −1, cardiac stroke volume (SV H)=0.2 ml kg −1 min −1, dorsal aortic blood pressure (D BP)=34±1 mm Hg, ventral aortic blood pressure (V BP)=45±1 mm Hg, and venous oxygen partial pressure (P VO 2)=26±2 mm Hg. Initial 1-h mean±S.D. chemical gill extraction efficiencies (EE) for tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE) were 42±8, 58±16, and 68±17%, respectively. Forty-eight hour EE of 9±1% for TCE (log K OW=2.39) and 21±4% for PCE (log K OW=3.06) indicated they were approaching steady-state, in contrast to 54±13% for HCE (log K OW=4.04) which was not near steady-state. The EE for all three chloroethanes were significantly ( P<0.05) different from each other from 24 h to 48 h. Forty-eight hour lake trout mean cumulative chemical clearance (Cl X) values for waterborne TCE, PCE, and HCE were 64±11, 120±14, and 226±29 l kg −1, respectively. Lake trout Cl X and Q W for TCE, PCE, and HCE demonstrated an approximate 1:1 relationship indicative of water-flow limited gill absorption. Chemical gill absorption observed for the lake trout and chloroethanes was similar to the rainbow trout ( Oncorhynchus mykiss) from previous investigations and provided further support for the water-flow limited model of chemical flux across fish gills for mid-hydrophobic chemicals (log K OW=3.0–6.0).