288 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



organic bodies which find such conditions favorable, but at the same 

 time many of these organisms, particularly the diatoms and zoospores, 

 are attracted to the surface by the sunlight and are thus placed beyond 

 reach of the oyster. In rainy or stormy weather, however, they are 

 driven down toward the bottom, where they may be brought witlini the 

 influence of the cilia, and at the same time there is an increase in the 

 amount of other organic sediment, much of which is available as food. 



Shallow water, as a rule, produces more food than the greater 

 depths, owing largely to the fact that it warms more quickly and thus 

 increases the vitality of both the oyster and its food. The latter shows 

 its greater vigor by a more rapid multiplication, and the former by its 

 greater consumption of the food which is thus provided for it. In other 

 words, the chemical and physiological changes resulting in the conver- 

 sion of inorganic matter into oyster tissue through the medium of plant 

 life go on more rapidly in the presence of warmth. It must also be 

 remembered that the shallow waters are generally of a lower density 

 than the deeper ones, and this aj)iiroach to brackishness appears to be 

 also favorable to the production of food. 



Summer and fall, the seasons of most vigorous growth of aquatic 

 vegetation, are in most localities likewise the best seasons for the 

 growth of the oyster, while in winter the food supply is at a minimum, 

 the vital activities of the oyster are much reduced, the ciliary action is 

 weak, and the oyster in a state of semihibernation, both the waste and 

 repair of tissue being reduced to a minimum. 



That the oyster in many places reaches its greatest fatness and per- 

 fection late in fall is due partly to the quantity of food produced during 

 the summer and i)artly to the cessation of the drain which the act of 

 spawning entails. Shortly before and during the spawning season 

 most of the nutrient matter in the food is utilized in the rapid growth 

 of the sexual products, but after the cessation of spawning it is con- 

 verted into surplus protoplasmic matter, which is stored up in the 

 tissues and thereby renders the oyster fat and well flavored. 



ENEMIES. 



At all stages of its career the oyster is preyed upon by more or less 

 dangerous foes. It might be supposed that an animal inclosed in a 

 ponderous armor, which in times of danger is a complete encasement, 

 would be free from the attacks of enemies, but no organism has ever 

 evolved a protective device which some other organism has not found 

 partially vulnerable; and it must be remembered that the oyster is not 

 always as well protected as we find it in the adult and marketable con- 

 dition. In the young state, before attachment, the minute and delicate 

 fry is fed upon extensively by the adult oyster and by other mollusca, 

 lingulas, worms, sponges, and hydroids. Upward of 200 young have 

 been found in the stomach of an oyster, and there is but little doubt 

 large numbers are so consumed on every oyster-bed. Probably the 



