Fig. 5. (A) Effect of the water flow rate on dissolved oxygen (DO) concentration in the boundary layer in 29 d.p.f. rainbow trout embryos before hatching relative to the distance to the chorion. Values are means ± s.e.m., N=6. The DO was measured in the same six embryos at the three different flow rates, starting with the highest rate. Flow rate values represent the flow in ml min^–1 (7.2, 5 and 3) entering the experimental chamber (3.3 cm widex2 cm deep). (B,C) The boundary layer gradient (% sat, the difference between the DO in the free-stream and the DO at the surface; B) and the boundary layer thickness (BLT; C), were calculated from the boundary layer curves in A and are plotted against flow rate.