170 MARINE PRODUCTS OF COMMERCE 



including nothing larger than fish a couple of inches long. On the other hand 

 the deep-sea swallowers are known to ingest fish exceeding their own length. 

 The writer once took a tropical fresh-water goby, the gauvina, Eleotris pictus, 

 14/2 inches long, which had swallowed another goby, Gobiomorus maculatus, 

 8/2 inches in length. The head of this morsel was at the vent of the swallower 

 and partly digested, while its tail was visible in the mouth of the larger fish. 

 There are cases on record of fish that died in the effort of swallowing fish too 

 large for them. The writer once had in his possession a large-mouth black 

 bass, Micropteriis salmoides, which evidently had choked in the endeavor to 

 swallow another bass of its own kind, which was not much smaller than itself. 

 In this case the tail of the smaller fish projected 3 or 4 inches from the mouth of 

 the larger one. The Smithsonian Institution has on exhibit a 12-foot fossil skeleton 

 of an extinct fish, Portheus, which died millions of years ago. Inside it is the fossil 

 skeleton of a 6-foot specimen of the same species. It seems probable that the 

 larger fish died because of its gluttonous cannibalism. 



It has been shown that some fish feed on other fish and some on lower animals. 

 The question as to what the lower animals feed on logically comes to mind. It 

 may be said at once that, although animals may prey upon one another, the 

 original source of their food consists of plants. In other words, "All flesh is grass," 

 and at the bottom of the pyramid of fish food are plants. The most important 

 are the single-celled microscopic plants, especially the diatoms. This is true be- 

 cause nearly all marine fish during their larval stages feed on minute plants. 

 Indeed, some highly important commercial species, as the common herrings, 

 Clupea, the menhaden, Brevoortia, and quite a number of others, feed on such 

 organisms throughout life, while the vast majority change to a diet consisting of 

 larger animals and plants. Similarly, the mollusks, crustaceans, and other forms 

 of animal life that enter into the diet of fishes feed on single-celled plants in the 

 larval stages. As in fishes, some forms never change from that kind of diet, 

 while others eat larger organisms during their adult life. 



This interlocking and intimate relationship of food among the various groups 

 of aquatic animals has frequently been overlooked, or at least insufficiently con- 

 sidered, for the welfare of our aquatic resources. Too often, organic pollutions 

 and chemicals discharged into ponds, lakes, streams, and arms of the ocean have 

 been considered harmless unless fish were killed outright. Such a line of thought 

 obviously ofi^ers false security, for it is evident from what has been said already 

 that if one 'link" breaks in the "chain" of food supply the fish population in that 

 vicinity is doomed. It is entirely possible, of course, that the adults can with- 

 stand the pollution and obtain ample food for a time, but their young, and the 

 young of the creatures upon which the adult fish feed, may be deprived of the 

 necessities of life. If that is the case, such a polluted locality will produce no fish. 

 It is evident, then, that the effects of pollutions is a difficult and complex study, 

 to which too little attention has been given. 



Migrations 



The long migrations from the sea to the headwaters of rivers, made by some of 

 the Pacific salmon (Oncorhynchus) have long amazed everyone. Those in- 

 dividuals of the king salmon that ascend to the headwaters of the Yukon River, for 

 example, make a journey of a couple of thousand miles, fighting their way up 



