142 THE WEALTH OF THE SEA 



feeding on plants are referred to as herbivorous 

 fishes. 



The size of the fish generally offers no suggestion 

 at all as to the kind of food consumed, because some 

 large fish feed only on minute organisms, whereas 

 some small ones feed on comparatively large forms 

 of life. The structure and size of the mouth, the 

 teeth, the gill-rakers, and the alimentary canal, how- 

 ever, frequently afford a clue to the general type of 

 food eaten. To determine the particular animals 

 and plants upon which the various species subsist 

 is much more difficult, for it requires an examination 

 of the contents of numerous stomachs. Certain 

 species, as for example the menhaden and the mul- 

 lets, feed on minute organisms. In the study of the 

 stomach contents of such fishes a microscope is re- 

 quired. This adds to the difficulty and greatly to 

 the tediousness of the work. In those species which 

 feed on large foods, the undigested parts often are 

 fragmentary, making identification difficult and un- 

 certain. Furthermore the food of the young usually 

 differs very considerably from that of the adulis, 

 and not infrequently stomachs are empty. 



It is an interesting fact that whereas some species, 

 including large ones, feed on microscopic organisms, 

 others take tremendously large forms in proportion 

 to their size. Certain fishes at times have been known 

 to swallow other fish longer than themselves. The 

 writer once caught a tropical fresh-water goby four- 

 teen and a half inches long which had partly swal- 

 lowed a goby of a different species eight and a half 

 inches in length. The head of this "morsel" was in 



