144 GIANT FISHKS 



the motive power to propel the fish forward. The skin, with 

 its tiny scales, offers practically no resistance, and the chances 

 of friction are further minimized by the presence of a copious 

 supply of slimy mucus which covers the surface of the body. 



The Tunnies are essentially fishes of the open sea, but 

 frequently approach the coast when the weather is calm and 

 comparatively warm. They are great wanderers, and roam 

 far and wide in search of prey, sometimes travelling for con- 

 siderable distances at high speeds. It has been noticed that 

 a Tunny can keep alongside a ship travelling at 8 knots without 

 apparent effort. These great fishes may often be observed 

 leaping about at the surface in pursuit of their food, or swim- 

 ming along leisurely with the tips of their fins projecting from 

 the water. They are always on the move, roving in every 

 direction and relentlessly chasing surface fishes like the herring, 

 sardine, flying-fish or mackerel, which, with squids and cuttle- 

 fishes, provide their favourite diet. " Savage and predatory," 

 writes Professor Roule, " they give chase ceaselessly to the 

 smaller fishes. ... In this domain, which extends in depth 

 as well as in area, they are the wolves, the foxes of the steppes 

 and forests, only more in number and swifter in movement. 

 They display the same supremacy in gluttony, though upon 

 a greater scale, and only yield the palm to the sharks, which 

 are even more powerful than themselves". There is, however, 

 one other monster of the sea which is greatly feared by the 

 Tunny, and that is the Killer Whale, which has been known 

 to seize and devour these great fishes. 



The Tunnies, and perhaps a few of their relatives, are 

 unique among fishes in possessing a body temperature which 

 is three degrees or more above that of the surrounding water — 

 that is to say, they are warm-blooded fishes. This peculiarity 

 is perhaps associated with their tremendous muscular activity. 



From the time of Aristotle the migrations of the Common 

 Tunny have always been a subject of interest and speculation. 

 It was early observed that the shoals made their appearance 

 in a given locality with gieat regularity at a certain season, 

 and, after a stay varying from a few weeks to several months, 

 departed almost as suddenly as they had arrived. Whence 

 they came and where they were going was a mystery, and 

 many theories, some of them quite unsupported by any sort of 



