VOLUMETRIC STUDIES OF THE FOOD AND FEEDING 



OF OYSTERS. 



By H. F. MOORE, 

 Assistant, United States Bureau of Fisheries. 



Economically considered, probably the most important direct interrela- 

 tion between a marine animal and plants is that existing between the oyster and 

 its food. We have in the United States alone an industry valued at $18,000,000 

 per annum, which is immediately dependent upon the supply of microscopic 

 vegetation in our bays and estuaries, a vast food resource useless to man in its 

 original state, but of great present and still greater potential value when trans- 

 substantiated into the flesh of oysters, clams, and other moUusks. 



Various investigations have shown that about 95 per cent of the food of the 

 oyster consists of diatoms and that most of the remainder is composed of other 

 equally minute plants or organisms on the more or less debatable borderland 

 between plants and animals. The oyster obtains these microscopic organisms 

 by drawing feeble currents of water between the open shells, straining them 

 through the exceedingly minute orifices in its gills, and passing the filtrate by 

 ciliary action into its mouth, which lies ensconced between two pairs of fleshy 

 palps close to the hinge of the valves. Though the currents induced are feeble 

 they are constant, and during the course of twenty-four hours the water thus 

 minutely strained is many times the volume of the oyster. 



It is common knowledge among oystermen and oyster growers that differ- 

 ent localities diff'er markedly in their powers or capabilities for growing and fat- 

 tening oysters, and the results of various researches have shown that these 

 diversities are correlated with the amount of food available to the sessile oys- 

 ters. A deficiency may be due to a natural poverty of the waters, to an over- 

 population of oysters, or to an absence of currents sufficient to carry the food 

 within reach of the feeble external currents set up by the oysters themselves. 

 Frequently all three of these factors are found to be involved where oysters grow 



slowly and fail to fatten. 



1297 



