AQUATIC RESPIRATION OF FISHES 



Secondary folds 



15 



Distance along 

 secondary lamella 



(c) (d) 



Fig. 3. 



(a) Diagram to illustrate the counter-flow across a gill filament. 



(b) Profile of the sieve provided by secondary lamellae of three 



adjacent filaments. The water passes at right angles to the plane of 



the paper, (c) and (d) Theoretical graphs of the change in percentage 



saturation of the water and blood with oxygen during their passage 



across a secondary lamella. It is assumed that both fluids move at the 



same speed and have equal O2 capacities. The flow is counter in (c) 



but parallel in (d). (a and b after Hughes, 1961 .) 



utilisation of the oxygen. When the direction of water flow is 

 experimentally reversed in a tench the utilisation falls below 



10%. 



(iii) The water flow across the gills 



So far we have assumed that all the water flows between the 



