354 



THE BIOLOGY OF MARINE ANIMALS 



residing in the protein fraction. These fish are not responsive to water which 

 has contained food fish. Dogfish and teleosts cease to respond to hidden 

 food when the nostrils are plugged or the olfactory nerves severed (22, 



109, 117, 152). 



The role of smell in orientation is indicated by conditioned responses 

 to naturally occurring environmental odours. Salmon can detect stream 



Fig. 8.32. Olfactory Epithelium of Petromyzon 

 (after Ballowitz and Plate.) 

 Siz, sense cells; Stz, supporting cells; B, boundary of subepithelial blood space. 



odours and discriminate between then, an ability which may be of value 

 during migration. Pond minnows (Hyborhynchus) are able to discriminate 

 between the odours of different aquatic plants (64, 145). 



In behaviour studies involving conditioning, Bull (21) has demonstrated 

 that many species of marine teleosts are able to detect very small changes 

 in acidity and salinity. Positive conditioned responses were obtained in 

 many species to changes of pH 0-1 or more, and most fish could detect^ a 

 change of pH 0-04-0-06. Salinity changes of the order of 0-06% o to 0.45% o 



