10 FISHES AND FISHERY METHODS 



added when the fish moves into depths of higher pressure, and gases are 

 removed when the fish travels to regions of less pressure. Through the 

 function of the air bladder, the fish is capable of maintaining energy 

 expenditure. The air bladder also functions as a sound receptor, and in 

 some fishes as a sound producer, as a lung, and in sensory functions^. 



Respiration 



The gills of fishes are analogous to the lungs of higher vertebrates and 

 serve as an organ of respiration. Free oxygen enters into the circulatory 

 system, and carbon-dioxide is expelled through the slender gill filaments. 



Migrations 



The migrations of fishes is a topic which is of considerable interest to 

 the general public, and the homing of salmon to parental streams is well 

 known even to the school boy. In recent years it has been found that the 

 Pacific salmon (Oncorhynchus) inhabit the ocean waters at great distances 

 from shore through most of their marine life, and on approaching maturity 

 migrate vast distances to the rivers of their birth. Although homing is 

 well developed in the salmon, some straying to other streams does occur. 

 The king salmon is known to migrate even to headwaters of large rivers 

 such as the Columbia, Yukon, and Sacramento. Fish such as salmon, and 

 shad (Alosa sapidissima) , which migrate up rivers to carry out spawning 

 are referred to as anadromous forms, and fish such as the eel (Angiiilla) 

 which migrate from fresh water to salt water to spawn are referred to as 

 catadromous. 



Although the homing of salmon to their parental stream is one of the 

 most often discussed migrations of fishes, many marine forms show similar 

 spectacular migratory patterns. Atlantic cods undertake extensive migra- 

 tions. Such migrations include movements to and from nursery or feeding 

 areas and distance migrations such as from West Greenland to Iceland 

 and from the Norwegian Coast to the Berents Sea^l For some of the 

 tunas the migrations may be transoceanic. Albacore {Thunnus alahmga) 

 tagged off the Pacific Coast of the United States^ have been recovered 

 off the coast of Japan. Not all tunas, however, seem to display extensive 

 migrations. The yellowfin {Neothunnus macropterus) of the eastern Pacific 

 do not appear to be involved in transoceanic movement. At least one 

 species of Pacific flounder, Eopsetta jordani^, has l)een noted to undertake 

 rather extensive migrations along the coasts of Washington (U.S.) and 

 British Columbia (Canada), the movement being north in the summer 

 and south during the winter months. There is some evidence that the 

 adults of this species may return each year to the same spawning area. 

 Sharks may also undertake long migrations, and there is at least one 



