CULTURE OF FRESH-WATER MUSSELS. 85 



sumed for human use, provision is made to insure the perpetuation of the stock. In 

 nature the dominant animals are the mammals which apply the principle of protection 

 in the care of their young. Likewise among plants, those lines that have adopted this 

 economy have attained dominance. 



By the "artificial propagation method" the young mussel is carried through one 

 critical event (infection) only. Liberation from the host and the early juvenile stage are 

 equally if not more critical. Evidence showing this has been given above, and corrobora- 

 tive of this is the following testimony of Prof. Kellogg (1910) regarding the correspond- 

 ing stage in the soft clam : 



Probably not even the swimming stage is more critical for Mya than this period of creeping which is 

 of longer duration. It is exposed to numerous enemies and has little defense against them , for its trans- 

 parent shell is still very thin and brittle. 



Lefevre and Curtis (1912, p. 192) say regarding this stage of fresh-water mussels: 



It is to be supposed that only a very small proportion of individuals thus liberated would succeed 

 in reaching maturity, as they would be exposed to the same destructive agencies as are encountered 

 under natural conditions. 



The results attained in the present investigation seem to indicate that a culture 

 carried at least through the early juvenile stage and possibly to the adult stage would 

 be economically practicable. In the floating crate method and the ponds ' we seem 

 to have found methods of protection. The proportion of survivals (8 plus per cent) in 

 the crates is apparently greater than from those raised in the ponds (according to the 

 best records we have) and doubtless can be greatly improved upon. Compared with 

 the number under analogous conditions in nature it is tremendous. For example, 

 Prof. Mobius (1877) finds that a young oyster has 104 ^ 000 of a chance to survive and 

 reach maturity. The same is true among practically all forms in which the young are 

 early exposed to the vicissitudes of a free life. In the culture of sea clams the operator 

 is dependent for planting upon such seed clams as are obtainable from a purely natural 

 and thus somewhat uncertain supply. There is this decided advantage in operations 

 with fresh-water mussels, that the necessary glochidia can be obtained with practical 

 certainty as long as adult mussels last. 



Protection at other than the two critical periods mentioned would be included in a 

 complete system of culture. During the parasitic period it would consist in the proper 

 care of the host fish. It may be noted that the fish when infected demands reasonable 

 care, as the attaching glochidia cause a certain amount of laceration of the gills which 

 subjects the fish to possible infection from fish mold (saprolegnia) and doubtless to 

 some exposure from bacterial invasion. 8 



Culture for the adult mussels consists in providing the best environment for growth 

 as well as economical means of protection and recovery. Experience has shown that 

 other things being equal more rapid growth and development of heavier shell occurs in 

 flowing water than where a current is lacking. (For other factors, see "Habitat," 

 p. 94, Coker, Shira, Clark, and Howard, 192 1.) 



7 The recent results described under troughs and pens have yielded even larger percentages. 



8 Bacterium columnaris Davis has caused considerable mortality in experimental work at Fairport. 



