PROBLEM I. The Kinds of Animals of the Earth 



33 



Fig. 46 Fish move by means of the muscular tail to which the broad tail fin is attached. 

 They have other fins, both paired and unpaired, which are used principally for 

 balancing, (new york zoological society) 



two and a quarter billion people in 

 the world. But that is a tiny number 

 compared to fish populations. Of the 

 herring, alone, man catches and kills 

 about eleven billion each year. It has 

 been estimated that 200 billion other 

 herring are eaten annually by larger fish. 

 Yet the ocean remains well stocked with 

 herring. Twelve thousand different spe- 

 cies of fish have been described. They 

 range in size from the large tuna fish, 

 which weighs three quarters of a ton, 

 to the guppy of your aquarium which 

 measures a scant inch and weighs so 

 little you could not feel its weight in 

 your hand. 



Some interesting fish. The flatfish, 

 that is, the flounders and the soles, are 

 curiously built. They are extraordinarily 

 flat from side to side and spend most 

 of their time lying on one side half 

 buried in the sand. Both eyes are on 

 one side, the side which is always up. 

 In the young fish the eyes are where you 

 would expect them to be, one on each 

 side of the head. Then one eye moves 

 around and joins its mate. 



You may have heard of "flying fish," 



but fish cannot really fly. All fish, when 

 swimming rapidly, push themselves 

 through the water entirely by means of 

 their muscular tails. When near the sur- 

 face this motion of the tail may drive 

 them out of the water, so that fish are 

 often seen jumping. The flying fish have 

 very long paired fins which they spread 

 as they jump. Thus, they glide through 

 the air. Among the strangest fish are 

 those that can breathe by means of 

 lungs. They also have gills. Plan to do 

 Exercise 13. 



Fish migration. Fish migrations are as 

 interesting and as puzzling as are bird 

 migrations and, naturally, much more 

 difficult to study. Although eels had 

 been known and caught as a food fish 

 for thousands of years, until about 

 thirty-five years ago no one knew where 

 they laid their eggs or where the young 

 grew to be adults. Each fall thousands 

 of mature eels were seen to swim down 

 the fresh water streams of Europe and 

 America into the Atlantic Ocean. There 

 they disappeared. Finally a scientific 

 expedition tracked them to a region east 

 of the Bermuda Islands where they lay 



