8 FISHES AND FISHERY' METHODS 



rays the olfactory pits are located on the ventral surface of the snout. 

 Olfaction in fishes is important in determining certain behavior patterns 

 such as providing clues for orientation, searching for food, and avoidance 

 reactions. Chemoreception in the selachians and bony fishes is highly 

 developed, and experiments have indicated that the fish can detect 

 extremely small differences in concentrations of dissolved substances. 

 Brett and Mackinnon^ demonstrated that adult salmon were repelled by 

 water in which human hands had been rinsed, and Hasler^ relates an 

 experiment in which fingerhng salmon (Oncorhynchus) were capable of 

 detecting solutions of morpholene in concentrations as low as 1 X 10~^^ 

 ppm. 



Other Sense Organs 



Although fishes do not have external ears, an elaborate inner ear 

 (labyrinth) system exists. The labyrinth consists of two vertical and one 

 horizontal semicircular canals which connect to a membrane sac, the 

 sacculus, containing the earbone organs (otoliths). In the bony fishes 

 there is no direct connection with the exterior. However, in sharks and 

 rays there may be an external opening through a small duct. 



Lowenstein^" states the labyrinth has four functions: (1) to maintain 

 and regulate muscular tone, (2) to act as a receptor for angular accel- 

 erations, (3) to act as a gravity receptor, and (4) to act as a sound receptor. 



The lateral line system in fishes is normally well developed and may 

 be seen along the sides of most fishes. Most often the lateral line can be 

 seen starting back of the gill opening on the flanks of the fish and 

 extending back toward the caudal fin. In some fishes several lateral lines 

 may exist. Although not always detected, branches of the lateral line 

 extend onto the head. The lateral fine system acts in a sensory capacity 

 and is considered by most physiologists to be concerned with orientation 

 or "distant touch." Lowenstein^^ states that 'Tn aquatic environment 

 where optic orientation is of reduced accuracy, these organs are capable 

 of supplementing vision by helping to localize objects at a distance. These 

 objects may be moving (prey animals) and thus constitute the focal point 

 of a mechanical disturbance, or their presence and locahzation may be 

 perceived and computed from the time relations of reflected water waves 

 set up by the swimming movements of the fish itself.'' 



In the sharks and rays there is a system of jelly-filled canals in the 

 rostral region called the Ampulla of Lorezino. The exact function of this 

 canal system is not well understood. It has been suggested that it func- 

 tions in detecting changes in hydrostatic pressure. There is more evidence, 

 however, that it may be a thermoreceptor. 



