376 U.S. BUREAU OF FISHERIES 



University of Missouri have been grouped under the two headings, 

 mussel investigations and pollution studies. Attempts at artificial 

 propagation of mussels have led to a study of the effects upon aquatic 

 life of stream pollution by industrial wastes although these effects 

 are by no means confined to mussels but extend to the food and game 

 fishes as well. 



FRESH-WATER MUSSEL INVESTIGATIONS 



Mussel 2>ropagation expeHments. — The raising of large numbers 

 of fresh-water mussels in limited areas and with a limited water 

 suppl}^ which is being done successfully in the Fort Worth raceway 

 experiments, presents a series of problems concerning which little 

 or no data exist. Hence, a program of investigations was undertaken 

 over a year ago looking ultimately to the solution of the practical 

 problems of mussel farming. During the past year much progress 

 has been made in this work. To date the findings may be summarized 

 as follows: 



Physical and chemicaZ envirouTnent data. — A very complete set 

 of data on the chemical and physical features of the environment 

 suitable for the growth of fresh-water mussels has been obtained, 

 including continuous daily records of temperature, dissolved gases, 

 relative acidity, lime content, and other factors, for a period of over 

 14 months. These data have demonstrated that the calcium content 

 of the water can be controlled and a calcium level suitable for proper 

 shell growth readily maintained by the simple expedient of splashing 

 the intake water through piles of limestone rubble, as was done in 

 these experiments. From these records and analyses a set of normals 

 has been established against which conditions in other experiments 

 or even in other localities can be checked. 



Bottovi survival. — Commercially it is desirable that as large if 

 not larger mussel populations be maintained on a given area of bot- 

 tom in artificial raceways as would be found in natural waters. 

 However, in the raceway the volume of water available is much less 

 than in a natural river or stream. To determine, therefore, the bal- 

 ance between numbers of mussels per unit of bottom and amount of 

 water flow, experiments on this phase of the raceway problems were 

 undertaken. These experiments have yielded very definite results 

 and have made progress to the next development possible. 



The maintenance of projDer bottom conditions for mussels in arti- 

 ficial raceways requires the constant flow of a large volume of water, 

 so directed that the current will scour the bottom free of silt deposits. 



Deposition of even so small a layer of silt as one-quarter of an inch 

 in thickness, over the bottom of the raceway soon killed out even 

 the adults of most species of fresh-water mussels. The harmful ef- 

 fects of erosion silt were greatly increased by particles of decompos- 

 ing algae and other organic matter which in the undisturbed silt 

 deposits, created a high oxygen demand. These findings on erosion 

 silt and organic wastes confirm our previous statements, based on 

 field work in natural waters, concerning the elimination of mussel 

 beds in natural streams by silt deposits. 



The volume of water required for the power scouring of raceway 

 bottoms would be too large and too expensive to be practical under 

 most conditions of mussel farming, if large numbers of mussels are 

 to be handled in small areas and all of the available space utilized. 



