Fig. 3. (A) Effect of the chorion on dissolved oxygen (DO) concentration in the boundary layer in 31 d.p.f. rainbow trout embryos before hatching relative to the distance to the chorion (black circles, black lines) and in the same embryos after manually removing the chorion (red triangles, red lines) relative to the distance to the skin. Values are means ± s.e.m., N=5. (B,C) The boundary layer gradient (the difference between the DO in the free-stream and the DO at the surface in % sat; B) and the boundary layer thickness (BLT; C), calculated from the boundary layer curves in A. Ch (chorionated), animals with intact chorion; DCh (dechorionated), animals with chorion manually removed.