Fig.2. Plasma total ammonia content (A), plasma pH (B) and plasma [NH₃] (C) in rainbow trout exposed either to 288µmoll^-1 total ammonia for 24h (open bars) or to water with no added ammonia (filled bars). Values (mean ± S.E.M., N=6) are shown for fish swum for 24h at 0.75BLs^-1, at the swimming speed showing the lowest concentration of ammonia for each fish, and at U_crit. *Significant difference from the 0.75BLs^-1 overnight value (t-test, P<0.05); significant difference from the lowest plasma ammonia value (P<0.05).