INTERESTING CITIZENS OF THE GULF STREAM 



11 



Undersea Photograph by Dr. W. H. Longley 



PORTRAIT TAKEN BENEATH THE SURPACE OP THE SOUTH ATLANTIC 



Porkfishes and tang against a background of live coral six feet or more under water 

 among the Florida Keys. The shadowy object, suggesting an irritated porcupine, near the 

 lower right corner, is a purple sea-urchin with spines erect. 



widely known, and quantities of this fish 

 are shipped to distant northern markets. 

 For baking, a fine large one has few 

 equals. Bright red color in fishes has 

 often a peculiar significance, which will 

 be spoken of later. 



Though not exactly a snapper, the ex- 

 cellent table-fish known as the Yellow 

 Tail (Plate VII) belongs to the snapper 

 family. It is somewhat more elongated 

 than the true snappers, with lines more 

 graceful, and its tail-fin is more deeply 

 forked. One sees immediately that it is 

 a freer, swifter swimmer, navigating 

 wider stretches of more open water. 



WHY SWIPT SWIMMING FISH HAVE 

 PORKED TAILS 



Most marine animals which swim, es- 

 pecially swiftly and continuously, have 

 a forked tail-fin. This shape of tail 

 avoids the space immediately behind the 

 axis of the body where the stream-lines 



following the sides (of a moving fish ) 

 converge. A rounded or pointed tail 

 which would occupy such area would be 

 a drag. 



Whales and porpoises, though they 

 move the tail up and down instead of 

 from side to side, have a forked tail-fin. 

 only it lies in a horizontal instead of a 

 vertical plane. The wide ranging mem- 

 bers of the mackerel family and other 

 more or less related marine fishes have a 

 forked tail-fin set on a firm, narrow base : 

 and the freest swimming sharks (mack- 

 erel sharks and the Man-eater) have ac- 

 quired a tail of the same shape, though 

 the ordinary shark tail is weak and un- 

 symmetrical. 



Fresh- water minnows almost invari- 

 ably have a forked tail-fin, waters which 

 they have to traverse being considerable 

 in relation to the small size of the fishes 

 themselves. 



In the blues and screens of the waters 



