FRESH- WATER MUSSELS. 163 



chance of life that would ordinarily fall only to dozens. As previously pointed out 

 (p. 151), an extensive series of observations of fish reveals the fact that but few are 

 naturally infected with mussels and these usually in slight degree. The chance that a 

 large proportion of the glochidia discharged by any mussel will become attached to a 

 proper host is slight, and it is only because nature is prodigal in the production of glochi- 

 dia that the various species of mussels can maintain their numbers under natural condi- 

 tions. With the disturbance of natural conditions by the active pursuit of a commercial 

 shell fishery, nature's fair balance is destroyed, and some compensatory artificial aid to 

 the propagation of mussels is rendered necessary. 



It is not presumed that all the vicissitudes of mussel life are removed by the bringing 

 together of fish and mussel. Nature undoubtedly exacts heavy tolls at other stages. 

 Many of the young mussels on being liberated from the fish will fall in unfavorable 

 environments and meet an early death, while those that survive the earliest stage of 

 independent life may still be subjected to numerous enemies throughout the juvenile 

 period at least. Nevertheless, glochidia of certain species can be planted in such large 

 numbers and at such slight cost that, after making due allowance for an extraordinary 

 subsequent loss, substantial returns can be expected. That such results do obtain is 

 indicated both by experiments to be later described (p. 166) and by common experience 



MUSSEL CULTURE, 



The rearing of young mussels in tanks, in ponds, or (if under conditions of control) 

 in the river, may properly be termed "mussel culture," as distinguished from "mussel 

 propagation," which, as we have seen, consists in bringing about the attachment of 

 glochidia to fish and liberating the fish in public waters. For several years experiments 

 in mussel culture have been carried on by the Bureau of Fisheries at Fairport and else- 

 where, with a view both to securing irrformation regarding the life history of mussels 

 and to testing experimentally the possibilities of culture as a public measure of conserva- 

 tion or as a field for private enterprise. At first little success attended these efforts. 

 It was found that the mussels could readily be carried through the parasitic stage, but 

 that soon after leaving the fish hosts they perished. Apparently there was something 

 inimical to the young mussels in the artificial conditions of aquaria, tanks, or ponds, 

 although these might be supplied with rurming water derived from the natural habitat 

 of mussels. 



The first reported rearing of mussels under control was accomplished with the 

 Lake Pepin mucket in a crate floating in the Mississippi River (Howard, 1915). Ex- 

 periments initiated by the senior author in the ponds at Fairport, Iowa, about the same 

 time were also successful with the same species. Subsequently broods of the Lake Pepin 

 mucket have been reared from year to year by various methods. Less consistent results 

 have been obtained with the following river mussels: The pocketbook, Lampsilis ventri- 

 cosa, the pimple-back, Quadrula pustulosa, and until recently the yellow sand-shell, 

 Lampsilis anodontoides, and the mucket, Lampsilis ligamentina. Apparently the condi- 

 tions required for rearing the Lake Pepin mucket are less difficult to meet under control 

 than is the case with the other species mentioned. The reason is, doubtless, that Lamp- 

 silis luteola, being a lake-dwelling species as well as an inhabitant of rivers, is adapted to 

 more varied conditions. 



The methods employed in rearing mussels may be designated as follows: (i) The 

 floating crate with closed bottom (chiefly used in rivers) ; (2) the floating crate with open 



