144 U.S. BUREAU OF FISHERIES 



silt in screening and sorting light in river and lake waters, and the 

 changes in water temperature, dissolved gases, and other chemical 

 reactions of the river waters as a result of presence of suspended silt 

 have been determined. A report on the technical aspects of this 

 problem and application of these technical facts to the economic 

 fisheries problems produced by silt is now in preparation. 



In the course of the pollution studies methods for use of the plank- 

 ton animals as "index" or "test" animals in pollution studies have 

 been worked out. Both because of their economic importance as one 

 of the basic links in the food chain of most aquatic animals and 

 because of their physiological reactions, plankton have been found to 

 be very suitable for pollution tests. A discussion and description of 

 these methods is to appear shortly in a technical journal. 



In connection with both the Idaho pollution studies and the gen- 

 eral survey of the Mississippi River and its tributaries, large series 

 of experiments dealing with the effect of lead, zinc, ammonia, sulphur, 

 and various specific substances present in particular types of indus- 

 trial wastes have been made on fishes, fresh-water mussels, plankton, 

 and other aquatic animals. These tests have provided basic infor- 

 mation for the evaluation of pollution findings not only in the specific 

 cases involved but for future investigations. 



MUSSEL PROPAGATION 



During the year 1932 a large-scale experiment carrying with it 

 various appended studies on the growth, survival, feeding, and general 

 health of fresh-water mussels, both juvenile and adult, in confined 

 areas where the particular environment can be specifically controlled, 

 was begun at the Fort Worth station of the United States Bureau of 

 Fisheries. Raceways having various types of bottoms over which 

 water of different depths is maintained have been planted with young 

 and adult mussels of various species. Not only have the economic 

 species of Texas been planted in these raceways, but shipments of 

 important species from Indiana, Iowa, Arkansas, Illinois, and Mis- 

 souri have also been made to Fort Worth. 



The particular objective is the determination of the maximum 

 number of fresh-water mussels which may be raised successfully in a 

 given area by artificial propagation, artificial planting, and from 

 selected brood stock. By means of special apparatus continuous 

 series of observations on water conditions, food requirements, growth, 

 and activities of these mussels are being obtained daily by an inves- 

 tigator detailed to this laboratory. Since each mussel is marked, the 

 relative death rate of the various species and state of health and growth 

 of each individual are being checked from week to week. At inter- 

 vals the raceways are emptied of water and the mussel population 

 inspected directly. 



As this experiment must be continued over a period of 2 to 3 years 

 before final results can be stated only an advance report can be given 

 at the present time. Gratifying results, however, have been obtained 

 in the growth, crowding, and feeding tests, and these findings at 

 present seem to indicate that a very large number of mussels may 

 be successfully crowded into a small space if proper water and food 

 conditions are maintained. At present over 6,000 adult mussels are 

 under observation in these raceways as well as various plantings of 

 young. 



