CULTURE OF FRESH- WATER MUSSELS. 77 



tions. It should be possible to maintain such conditions by thoroughly cleaning the 

 walls and bottom each season and, so far as possible, excluding pond plants and animals 

 during the critical period when the young mussels are escaping from their hosts. 5 



GROWTH IN EARTH PONDS. 



A large plant of Lampsilis luleola was made in an earth pond in 19 14 from crappie 

 of two species, Pomoxu annularis and P. sparoidcs, and the sunfish, Lepomis pallidas. 

 The following spring an examination of the bottom yielded some eight mussels, the 

 largest 24 millimeters in length, the smallest 12. The growth was not as great as that in 

 the floating crate, but compared favorably. The number surviving, however, compared 

 with the thousands introduced into the ponds by means of the fish, was disproportionately 

 small. 



In lowering the water level of the pond there were found afewsheepshead, Aplodinotus 

 grunniens, whose presence was quite unexpected and contrary to the plan of the ex- 

 periment. As this is a mussel-eating fish, its presence might explain the disparity 

 in numbers of the young mussels. Fortunately, a smilar plant was made the same 

 season by the fish-cultural staff at the suggestion of the director. Since the pond 

 was larger and the total number which was recovered was greater, it will better rep- 

 resent the results by the pond method. 



A number of black bass were infected with Lampsilis luleola in the fall of 1913. In 

 the spring they were placed in one of the large earth ponds, 0.S43 acre in extent, used 

 for propagation. The following November (1914), when the pond was drawn, some 60 

 mussels were picked up from the bottom. In the spring of 1915 more were recovered, 

 making a total of 150. These were examined and measured. They had attained about 

 the same growth as the mussels in the floating crate. The largest measured 35 milli- 

 meters in length, the smallest 15.5." The greater length would be explainable as due 

 to the longer growth period; having been on the fish during the winter, they would in 

 all probability have completed their parasitic development some time before June 10, 

 the date on which the plant in the floating crate was made. As compared with the 

 small pond, the size doubtless contributed to the maintenance of more favorable condi- 

 tions. We have in such a body of water conditions closely approaching the habitat of 

 L. luleola in nature. Whether the distinctively river-growing mussels would thrive in 

 such a pond in the absence of a current has not yet been satisfactorily determined. 

 However, the fact that, in spite of many failures with some of these species, a few of 

 these (represented in fig. 73) have been found in the ponds, for the most part of unin- 

 tentional or sporadic occurrence (see Coker, Shira, Clark, and Howard, 1921, p. 165), leads 

 one to believe that favorable results might be obtained by a proper control of conditions. 



GROWTH IN PENS. 



Recently a device was employed by Roy S. Corwin (1920) at Lake City, Minn., 

 which gave very satisfactory results with the Lake Pepin mucket. A box 10 by 10 

 feet square and about 8 inches high was surmounted by chicken wire and the whole 



* Experiments planned to conform as closely as equipment permitted to the conditions proposed were carried through the 

 season of 1919. Precipitation of silt occurred in large Quantity, which doubtless accounts for failure to secure a plant of river 

 mussels. A plant of lake mussels (L. luteola) was obtained. 



'Measurements of these mussels after a second summer's growth. Deer, 191.;. give for trie largest a length of 65.6 millimeters. 

 From two of these were cut r6-line buttons 2 lines thick. (See footnote, p. 71.) 



