76 



BULLETIN OF THE BUREAU OF FISHERIES. 



previous fall and this pond was filled for the first time a few days before the plant was 

 made, it seems likely that rhabdoccels and similar enemies had not yet become established. 

 The number of successful sets observed in the case of newly established ponds (see earth 

 ponds) leads to the conclusion that this factor of "newness" 4 may be very important. 



In Table 5 below are given the measurements of 10 of these shells, including the 

 largest and smallest. There is given the increase per year as indicated by the winter 

 rest line. 



Table 



Irowth of 10 Mussels Quadrula Pustulosa, During Four Years in a Concrete- 

 lined Pond. 



The largest mussel of this series reared in a pond is considerably smaller than a 

 mussel of about the same age grown in the river, as shown by the following figures: 

 Pond grown, length, 24 millimeters; weight, 1.9 grams. River grown, length, 28 milli- 

 meters; weight, 4.6 grams. The retarding effect of the artificial conditions is obvious 

 enough in this comparison, where the advantage of selection is all in favor of the pond- 

 grown shell and in which the river-grown shell is a few months younger. 



In the summer following the discovery of this "set" of juveniles experiments were 

 carried out to determine if the results could be repeated. The conditions as to bottom 

 and clarification of water and source of water supply were made to coincide as closely as 

 possible with those of the successful ' 'set." In one respect only as far as known was there 

 a difference, namely, in regard to the factor of "newness" or absence of pond conditions. 

 The water was taken from the same reservoir which, having been in use four years, 

 had in a measure acquired the characteristics of a standing body of water. This difference 

 was realized, but it seemed best to make use of the established system of supply as long 

 as its suitableness was not disproved. Three species of mussels were used and several 

 plants made with each. These species were Lampsilis ligamentina, L. anodonloides, 

 and L. hdeola. The results were negative except with L. luteola, which, as indicated 

 elsewhere, is not a typical river mussel and has yielded successful sets in almost all 

 instances under the conditions prevailing in the ponds at the Fairport laboratory. 

 These results would seem to indicate at least that the conditions provided were not 

 decisive factors in the one successful set of Quadrula pustulosa, and that possibly the 

 one factor in question, namely, the water supply, is the one which was responsible for 

 success or failure. 



A review of the results attained in this type of pond, with its successful plants 

 among the failures, holds out some hope still for the solution of the problems of rearing 

 the true river mussels. The line of procedure indicated would seem to be the provision 

 of a water supply direct from the river and a rigid exclusion of established pond condi- 



1 The condition of the water supply beiore typical pond conditions have time I" develop. 



