igo BULLETIN OF THE BUREAU OF FISHERIES. 



ing time of the Unionidae. A law, however, which would close a river or large section of 

 a river for a period of five years or more would be most beneficial, for in that time much 

 could be accomplished both by artificial and by natural means to restore normal conditions. 

 Even artificial propagation, unaided by certain protective measures, could hardly be- 

 come effective on however extensive a basis it might be carried on, for unless some 

 means can be devised for saving the young mussels it is difficult to see how much head- 

 way could be made against the destruction of the supply. It therefore becomes of vital 

 importance not only to make illegal the use of any apparatus which will catch or injure 

 young mussels, but to see that the law is rigidly enforced. 



Certain requisite conditions for the artificial culture of fresh-water mussels, based 

 upon our knowledge of their life history and habits, may now be briefly referred to. 



SELECTION AND MAINTENANCE OF A FISH SUPPLY. 



Although only a comparatively few kinds of fishes have been thus far used in our 

 experimental infections, and doubtless as our experience widens many more will be 

 found to be favorable for the purpose, success has been attained chiefly with the black 

 basses, rock bass, and the sunfishes. All of these fishes have proved to be extremely 

 resistant to the injurious effects of gill infections (practically all of the commercial 

 species of mussels have bookless glochidia, which are gill parasites) ; to be able to carry 

 large numbers of glochidia through the parasitic period ; and to be easily kept in confine- 

 ment — three necessary conditions for the success of propagation. It is to be hoped 

 that other fishes will be found to be equally useful, but at present those just mentioned 

 afford the most promising material for the work. As has already been shown, some 

 species of fishes are very easily killed even by light gill infections, while others, accord- 

 ing to our experience, have resisted all attempts to bring about permanent implantation 

 of glochidia on their gills. The latter is particularly true of German carp and catfishes. 



Fortunately, the basses and sunfishes can be obtained in large quantities without 

 serious difficulty. In the reclamation work conducted by the Bureau of Fisheries 

 along the upper Mississippi River, immense numbers of young bass are annually seined 

 from the sloughs and "lakes" into which they are carried when the river rises over its 

 banks during the flood stages of early summer. When the water recedes these young fish 

 are caught outside the banks of the river, and only the small fraction of them which is 

 reclaimed in the seining operations is saved from the wholesale destruction (fig. 67, 

 pi. xvi). There is no limit to this supply of material for the work of mussel culture, 

 and doubtless extensive use will be made of it at the Fairport station. 



Even more valuable for the purpose are the species of sunfishes which we have used 

 (probably other species of the same group are equally good), for, besides being just as 

 resistant and as readily infected as the black bass, they are more easily kept and are 

 less subject to disease in confinement. An adequate number of breeding ponds, in which 

 sunfishes could be left to multiply naturally, would insure a large and constant supply 

 of these fish for artificial infections. 



