l86 BULLETIN OF THE BUREAU OF FISHERIES. 



them to adult size within a short term of years. Accordingly, we have attempted the 

 introduction of Lampsilis ligamentina into one of the ponds where no mussels had ever 

 been found by placing in the pond several hundred fish well infected with the glochidia 

 of this species; but several examinations of the mud and silt from the bottom, made 

 during the 1 8 months following, have failed to show anything as a result of the experiment. 



The conclusions drawn from these observations are encouraging because they 

 indicate, first, that other species, like those of the genus Lampsilis, whose shells are of 

 excellent quality for the best of buttons, may be reared to commercial size in about 

 the same length of time, and, second, that restricted localities can be stocked with 

 mussels by the introduction of fish infected with glochidia. The members of the genus 

 Lampsilis have shells which are evidently not much heavier than the shell of Unio 

 tetralasrmts , a fact which better fits them for life upon soft bottoms where there is little 

 current, and in such locahties they often occur. They move about more actively than 

 the heavier shelled species and this, doubtless, enables them readily to seek out the 

 most favorable food conditions in any body of water, instead of remaining long in one 

 place where the conditions are very stable, as do the heavier shelled species. The 

 study of any mussel which can live in small ponds like those in question and from which 

 button shells can be obtained should be followed up with care, since the extensive 

 culture of mussels would be a far simpler matter in ponds than in any stream where 

 high and low water and the shifting of the bottom might so largely interfere with the 

 most carefully located beds. For this purpose the species of Lampsilis which give 

 good button shells would seem the most desirable, because they are better adapted for 

 the conditions and because our planting experiments indicate that they reach a market- 

 able size in a shorter time than the quadrulas. 



We feel that there is nothing discouraging in what is at present known regarding 

 the rate of growth under the average natural conditions. Moreover, it should be 

 remembered that in most invertebrates where the growth rate has been studied this 

 may be modified to an astonishing degree by the food supply and that the actual size 

 of an individual furnishes no trustworthy clue to its age. It is not at all unlikely that 

 proper study of the food and other conditions necessary for the maximum rate of growth 

 will enable us to obtain shells of commercial size in even slow-growing varieties within 

 a reasonable number of years. To judge from the supposed annual rings of specimens 

 taken in nature, Quadrula ehena may take from 20 to 30 years to reach, under natural 

 conditions, the size which is most desirable. The question whether this is a necessity, 

 or only a result of the poverty of food conditions which most mussels meet in nature, 

 is one which must wait upon the proper scientific analysis of the mussel's food and rate 

 of growth in this and other species, and there is no problem in connection with the 

 attempted artificial propagation which has more pressing importance. 



