122 American Fisheries Society 



flow, but rather a fair circulation of water. The varied 

 services of the current render it of special importance to 

 the culturist in the selection of a grant since the product- 

 ive capacity of clam flat depends almost wholly upon the 

 circulation of water. It is a well known fact that the 

 growth of the clam is more rapid where the water is in 

 constant motion than in still water, and it has been com- 

 monly considered that this difference is due to the in- 

 creased amount of food, the clam in the current receiving 

 the greater food supply. But rapid growth in a good cir- 

 culation of water is a more complex problem than a sim- 

 ple increase in the available food supply, and it is the 

 main object of this paper to show that our previous ex- 

 planation of the effect of current on growth is only par- 

 tially correct. Current affects the life and growth of the 

 clam in many ways, but chiefly by regulating (1) the food 

 supply, (2) the amount of available oxygen, (3) the feed- 

 ing habits, (4) the secretion of lime salts and (5) the 

 sanitary conditions. 



Food Carrier. — An important work of the current is 

 that of carrying food. The clam obtains its nourishment 

 from the microscopic forms, which are generally distrib- 

 uted throughout all waters, although different localities 

 vary in abundance according to the conditions favorable 

 for their reproduction. The growth of the clam, as with 

 lower animals, is directly proportional to the amount 

 of food consumed, and the animal situated in a current 

 naturally receives a greater food supply than one in 

 still water. For all practical purposes current means 

 food, and within certain limits the increase in current 

 indicates the increase in quantity of available food, thus 

 furnishing an approximate index of growth. Since the 

 clam is a stationary animal with a limited feeding range, 

 it is obvious that a maximum point of food assimilation 

 can be obtained, when the clam will be unable to take 

 in any more food from a swifter current. For this rea- 

 son the term current, as used here, implies only a good 

 circulation of water and not an exceedingly swift flow. 



