Fig. 2. (A–D) Effect of prolonged exposure to hypoxic water (35% sat) on dissolved oxygen (DO) concentration in the boundary layer of rainbow trout embryos before hatching relative to distance to the chorion (A–C) and in larvae after hatching relative to the distance to the skin (D). Numbers beside panel letters indicate developmental time in days post fertilization (d.p.f.). Values are means ± s.e.m., N=8; different animals were used at each developmental stage but the same animals were tested at 0.5, 4 and 8 h exposure to hypoxic water. (E,F) The boundary layer gradient (the difference between the DO in the free-stream and the DO at the surface; E), and the boundary layer thickness (BLT; F), were calculated from the boundary layer curves in B and C, and are plotted against time in hypoxic water (h). Changes during prolonged exposure were trivial at 11 and 50 d.p.f. and are not plotted in E and F.