AQUATIC RESPIRATION OF FISHES 



27 



Most fishes have mechanisms for cleaning and protecting the 

 gill epitheUa. In some teleosts, for example the carp family, the 

 presence of regular 'coughing movements' is well known. During 

 these movements the respiratory current is reversed to a greater 

 or lesser extent and under certain conditions the movements 

 may be very forceful. Among cartilaginous fishes reversal of 

 flow from the parabranchial cavities results in water being 

 forced out through the spiracles. It is a common sight when 

 skates and rays are flapping about on the deck of a trawler to 

 see water spouting out of their dorsally-situated spiracles. These 

 'spouting' movements form a regular part of the breathing 

 rhythm in these fishes, although their frequency is less when the 

 water they are inspiring contains little suspended matter. Dur- 

 ing these movements producing reversal of flow the externa] 

 openings of the gill slits or the opercular openings are actively 

 closed. In teleost fishes contraction of the adductor muscles 

 draws the filaments attached to each branchial arch closer to 



50 



^0 



(u 30 

 E 



o 

 " 20 



o 



^ 10 



50 



100 

 Minute volume 



150 



60 



AO 



20 



200 



ml. 



Fig. 9. 



Graphs to show the way in which the ventilation or minute volume 

 of a tench is increased partly by the frequency (crosses) and partly by 

 an increase in stroke volume. (Hughes and Shelton, unpublished.) 



