284 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



exposed to it, except when the currents are suflQcient to exert a scouring 

 influence. 



Large oysters are not so susceptible as small ones to the effects of 

 mud, but even those full grown may be stifled or buried by the rapid 

 deposit of mud or sediment, whether this be of organic or inorganic 

 origin. Freshets and heavy seas often cause great damage by the 

 amount of mud, sand, and other debris which they carry upon the beds. 



The question of the physical characters of a suitable bottom for 

 oyster-culture is considered in another connection. 



TIDES AND CURRENTS. 



Tides and currents are important factors in the growth and culture 

 of the oyster. They bring about the aeration of the water and oxida- 

 tion of its dead organic ingredients; they have a scouring action upon 

 the bottom and thereby cleanse the cultch, and at the same time serve 

 as the vehicles for the transportation of food, of the genital products, 

 and of the young. Stagnant water tends to become exhausted of its 

 oxygen; it is heated by the sun, and the contained organic matter 

 undergoing death and decomposition causes it to become foul and fatal 

 to the oysters in the vicinity. With curreuts, however, a fresh supply 

 of oxygen is constantly being supplied for respiration and for the 

 combustion of the efl"ete matter, which is thus rendered harmless. 



Over densely-populated beds the food supply, unless unusually pro- 

 lific, as in claires, would in time become exhausted. The oyster can 

 not, of course, change its location, but the same purpose is subserved 

 by currents constantly bringing a fresh supply of food-laden water 

 within the influence of the ciliary action by which the oyster captures 

 its food. 



The genital products of the oyster, both male and female, are sim])ly 

 discharged into the surrounding water. The eggs are absolutely immo- 

 bile, and while the spermatozoa, or male elements, possess the power of 

 locomotion to some extent, they are obviously incapable of moving very 

 far during the limited period of their mobility. In densely-crowded beds 

 no doubt a considerable proportion of the eggs may become fertilized 

 even without the agency of currents, but where, as upon most oyster- 

 grounds, the oysters are scattered, the proportion must be exceedingly 

 small. Oystermen are well acquainted with the fact that upon beds 

 removed from the influence of the tides the rate of reproduction is 

 very low. 



Currents, however, will bring about a distribution of the genital 

 products, more particularly the almost impalpable milt, and thus give 

 an opportunity for obtaining better results by increasiug the chances 

 for spawn and milt to come into contact. Although the young spat is 

 a free-swimming organism, yet its powers are not sufficient to carry it 

 to any great distance from its original source. It is transported mainly 

 by tidal currents, and, as a general rule, the more widely distributed 

 a given lot of spat, the greater is the number liable to become success- 



