66 BULLETIN OF THE BUREAU OF FISHERIES. 



and difficult. The improved float because of its form is more readily towed and handled 

 in the current than the very much smaller floats first constructed and may be easily 

 drawn out of the river by a team of horses when necessary, as for winter quarters. 



Other methods were employed in the investigation and, in a way, carried parallel 

 for comparison to test the possibilities of the equipment already installed at the biological 

 laboratory at Fairport. These were aquaria and indoor tanks and troughs, cement 

 ponds, and earth ponds. Each of these was supplied with running water except in the 

 case of special experiments with balanced aquaria. The water for the most part was 

 taken from a reservoir receiving its supply by pump from the Mississippi River. Thus 

 the water was, as a rule, practically unmodified. In some experiments with balanced 

 aquaria filtered river water was used in order to eliminate the predacious animals which 

 prey on the early stages of the mussels. For the same purpose, as well as to reduce the 

 amount of sedimentation in river water, specially devised settling tanks were employed 

 for supplying aquaria. 



The cement ponds (fig. 61) were of reinforced concrete 50 feet long, 10 feet wide, and 

 averaging 2% feet deep, having perpendicular sides and constructed for the temporary 

 retention of fish. An accumulation of mud and a specially prepared bottom of gravel, 

 together with an abundance of water plants, furnished conditions which proved suitable 

 for some of the most delicate species of fish. It was assumed that these conditions were 

 as suitable to the needs of the mussels as they could be made under the circumstances. 



The earth ponds were from 41 to 61 feet long and 24 feet wide, varying in depth 

 from 4 inches at the intake pipe to 4 feet at the well. An abundance of water plants 

 furnished food and shade for the fish. The cement and earth ponds as compared with 

 the floating crate do not so readily furnish the means for frequent observations of early 

 stages. In using them it was planned to test their possibilities of rearing clams by a 

 comparison of older juveniles grown in them. Thus the probable disadvantage of 

 frequent disturbance necessary in making observations on younger juveniles would be 

 avoided. 



Plants of young mussels were made from infected fish in each of the culture devices 

 mentioned. A modification of the cement pond was used in one instance for the purpose 

 of securing a current comparable in rapidity to that to which the river mussels are 

 accustomed. A flow of 50 gallons per minute was supplied to a trough 16 inches wide 

 by 12 inches deep by 50 feet long, giving a current of 0.1 mile per hour. This is by no 

 means equivalent to the 2 to 3 miles per hour of the Mississippi, but was planned to 

 imitate the conditions of the river more closely than that of the ponds in which the flow 

 is inappreciable. 



OBSERVATIONS ON GROWTH OF JUVENILE MUSSELS. 



In this investigation studies upon growth have been made with a view to securing 

 data upon general conditions as well as upon the more specific methods of rearing under 

 artificial environments. The species tested were chiefly heavy-shelled river mussels, 

 which include most of those that are considered of commercial value, as distinguished 

 from the thin-shelled pond-dwelling forms. The latter apparently offer no particular 

 difficulties. The most complete results were obtained from a species which selects a 

 habitat somewhat intermediate between these extremes, in that it dwells in lakes and 



