CHAPTER IX 

 TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



Page 



Transport of water __ 185 



Determination of tlie rate of water transport 186 



Direct metliods 186 



Constant level tanks 186 



Current indicators 190 



Indirect methods 193 



Use of turbid water 193 



Use of radioactive plankton 194 



Control of the rate of water transport through the gills 194 



Steady state 195 



Reduction of water transport 196 



Dissolved organic substances and rate of water transport 197 



Respiration __ 200 



Methods of study 201 



Microdetermination of oxygen 204 



Oxygen uptake _ 205 



Oxygen uptake under continuous pull of the adductor muscle 209 



Environmental effects 211 



Seasonal changes in the rate of oxygen uptake 211 



Effect of change in salinity and pH 211 



Respiratory quotient, R. Q 212 



Respiration In other species of oysters 212 



Utilization of oxygen 214 



Bibliography. ___ 215 



All bivalves maintain a steady flow of water 

 through their gills for feeding, respiration, and the 

 removal of products of metabolism. In the litera- 

 ture on oyster physiology this process is described 

 under such names as pumping, filtration, ventila- 

 tion, respiratory current, and feeding. When 

 "feeding" is used in reference to the transport of 

 water by the gills, tiie term is misleading since 

 feeding imphes the acceptance of food by the 

 organism and involves sorting and rejection of 

 particles removed from the water by filtration. 

 The terms ventilation and transport of water 

 appear to be suitable expressions for denoting the 

 processes by which the oyster mainfains a flow 

 of water in a comple.x system of water tubes and 

 through the epibranchial chambers. Both terms 

 are used in this text interchangeably, depending on 

 whether the emphasis is on collection of food or on 

 respiration. 



Maintenance of a steady stream of water and 

 respiration are the two principal functions of the 

 gin. Of lesser importance are the excretion 

 (through diapedesis) of certain products of 

 metabolism, tlie absorption of substances dissolved 

 in water, and the ingestion of particles settled on 



FISHERY bulletin: VOLUME 64, CHAPTER IX 



the gills by the leucocytes present on their surface. 

 Water transport and oxygen uptake are inter- 

 dependent functions that may be considered as 

 two phases of a single process. It is convenient, 

 however, to discuss them separately, keeping in 

 mind tliat both activities occur simultaneouslj'. 



TRANSPORT OF WATER 



The preceding chapter described how a steady 

 rate of water current inside the demibranches is 

 produced by synchronized beats along the thou- 

 sands of tracts of lateral cilia. Temporary cessa- 

 tion of ciliary motion along some of the tracts or a 

 disturbance in their rhythm of beating will result 

 in a drop of hydrostatic pressure inside the water 

 tubes and cause a leak of water through the ostia. 

 This disturbance may slow down or stop the 

 cloacal current. 



The adductor muscle, the edge of the mantle, the 

 gill muscles, and the ostia all pla.v a part in the 

 regulation of the flow of water produced b}' ciliary 

 activity. It is self-evident tliat, within the limits 

 determined by the capacity of the gills' chambers, 

 the volume of water transported depends on shell 

 movements and the width at which the two valves 

 are kept apart. When the shell closes the current 

 stops. A similar efl^ect may be produced by the 

 edges of the mantle independently of the move- 

 ments of the valves. Sometimes the pallium 

 assumes a vertical position and the tentacles along 

 tlie edges of the opposing mantles interlock while 

 the valves remain wide open. Under this condi- 

 tion no water penetrates through the curtain wliicli 

 seals the entire pallial cavity. This behavior 

 occurs in the presence of low concentrations of 

 to.xic substances and during the spawning of the 

 female oyster (ch. XIV, p. 304). It is, therefore, 

 obvious that shell movements should not be con- 

 sidered as indications of the feeding of the oyster, 

 a mistake which frequently is found in papers 

 describing the "feeding" of oysters. 



The rate of water transport may also be reduced 



185 



