REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. 191 



THE BEST SEASONS FOR INFECTIONS. 



It has already been stated that the duration of the parasitic period of the mussel is 

 inversely proportional to the temperature of the water. This fact is obviously import- 

 ant for mussel culture, since the longer the fish have to be kept while carrying the glo- 

 chidia the greater is the loss from disease and other causes. The loss not only involves 

 the fish but the potential mussels which they are nourishing as well. It therefore be- 

 comes desirable to reduce, as far as possible, the length of time that the infected fish 

 must be retained, and this we have seen depends upon the temperature. Late spring 

 and summer, consequently, are the seasons when the maximum efficiency from arti- 

 ficial infections should be obtained, for in the warmer water at that time the duration 

 of the parasitism will be at the minimum — about two weeks or even less. The glo- 

 chidia of Lampsilis are available all through the spring and as late as July, while those 

 of Quadrula can be obtained during the summer months, and most of the commercial 

 species of mussels fall in these two genera. Of course infections can successfully be made 

 in the fall and winter and the duration of the parasitism reduced by keeping the water 

 artificially warmed, but the difficulty of maintaining the fish alive under these con- 

 ditions is greatly increased. 



THE MUSSEL SUPPLY. 



By far the greater number of species of commercial value, as has already been stated, 

 belong to the genera Lampsilis and Quadrula, and, as both of these genera are widely 

 distributed, practically all of the mussel-bearing streams of the Mississippi Valley 

 may be drawn upon for a supply of material for cultural purposes. We have found 

 that living mussels may be shipped even long distances with little or no mortality, 

 especially in cool weather, and it is therefore possible to obtain breeding material from 

 places at quite a distance from the station where the infections are to be made, should 

 the local supply be inadequate. We have had on several occasions large numbers of 

 gravid mussels shipped from Terre Haute, Ind., to La Crosse, Wis., to Manchester, 

 Iowa, and to Columbia, Mo., with scarcely the loss of an individual, and have successfully 

 used the glochidia obtained from them in infecting thousands of fishes. 



According to our experience mussels thrive very well in confinement, in small ponds 

 and laboratory tanks, and that without any special attention to a food supply. We 

 have for years been keeping both pond and river forms alive in the laboratory for months 

 at a time in tanks containing a few inches of sand on the bottom and supplied by tap 

 water. Under such conditions mussels have frequently been retained in the laboratory 

 from the fall to the following summer. It should therefore be an easy matter to keep 

 mussels for breeding purposes in ponds with natural bottoms in any quantity desired, and, 

 if the ponds are fed with river water, a natural food supply should be present in abundance. 



Since, as has been pointed out above, the species of Quadrrila, Unio, and other sum- 

 mer breeders abort their embryos and glochidia with astonishing ease when disturbed, 

 it will be necessary, when making infections with the glochidia of forms exhibiting this 

 peculiarity, to collect the material at a time prior to the fertilization of the eggs and to 



