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First published online March 31, 2007
Journal of Experimental Biology 210, 1435-1445 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02754
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Parameters influencing the dissolved oxygen in the boundary layer of rainbow trout (Oncorhynchus mykiss) embryos and larvae

Cosima S. Ciuhandu1, Patricia A. Wright1,*, Jeffrey I. Goldberg2 and E. Don Stevens1

1 Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
2 Department of Biological Sciences, University of Calgary, Calgary, Alberta, T2N 1N4, Canada


Figure 1
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  		Fig. 1. (A–G) Effect of developmental stage and hypoxia on dissolved oxygen (DO) concentration in the boundary layer of rainbow trout embryos before hatching relative to distance to the chorion (A–E) and in larvae after hatching relative to the distance to the skin (F,G). Boundary layers were measured in normoxic water (100% sat, black circles and black lines) and after 30 min exposure to hypoxic water (35% sat, red triangles and red lines). 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 and different animals were used in normoxia vs hypoxia. (H,I) The boundary layer gradient, (the difference between the DO in the free-stream and the DO at the surface; H) and the boundary layer thickness (BLT; I), were calculated from the boundary layer curves in A–G, and are plotted against developmental time (d.p.f.). Vertical broken line indicates approximate time of hatching.

 

Figure 2
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  		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.

 

Figure 3
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  		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.

 

Figure 4
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  		Fig. 4. (A) The dissolved oxygen (DO) concentration ~100 µm inside the chorion in 31 d.p.f. rainbow trout embryos before hatching, and in the same embryos, the DO concentration in the boundary layer relative to the distance to the chorion. Values are means ± s.e.m., N=6. (B) The boundary layer gradient (% sat; to Ch, the difference between the DO in the free-stream and the DO at the surface of the chorion) compared with the gradient across the chorion (x Ch, the difference between the DO at the surface of the chorion and the DO inside the chorion).

 

Figure 5
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  		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.

 

Figure 6
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  		Fig. 6. (A) The number of movements min–1 by 44 d.p.f. rainbow trout larvae in normoxic water (first open circle), then exposed to 35% sat for 4 h (closed circles), and then returned (vertical broken line) to normoxic water for a further 2 h (open circles). Values are means ± s.e.m. (N=9). The effect of exposure to hypoxia was reversible, but there was a delay of about 30 min and then a gradual return to pre-exposure levels. (B) Time course of the change in DO (% sat) in the free-stream around the larvae while movements were being recorded.

 

Figure 7
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  		Fig. 7. Number of movements per 30 min (A) or per min (B,C) by rainbow trout embryos exposed to water with 100% (black circles), 50% (red triangles), or 35% sat (green squares) at three different developmental stages; numbers beside panel letters indicate developmental time in days post fertilization (d.p.f.). Values are means ± s.e.m. (N=6); note different scale on y-axis in A.

 

Figure 8
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  		Fig. 8. The relationship between gradient and boundary layer thickness (BLT) with oxygen uptake – both increased with an increase in oxygen demand. Oxygen demand is expressed as oxygen uptake interpolated from Rombough (Rombough, 1988aGo). Lines are least-square regression lines using the means at each developmental stage in normoxic water.

 

Figure 9
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  		Fig. 9. The relationship between the dissolved oxygen (DO) at the chorion of embryos (top broken line) or at the skin of larvae (bottom broken line) as a function of oxygen supply (DO in the free-stream). Broken lines are least-square regression lines using the mean values at each developmental stage; solid line to the origin is the unity line. Values are means ± s.e.m.

 




© The Company of Biologists Ltd 2007