36 U. S. BUREAU OF FISHERIES. 
MUSSEL SURVEY IN UPPER MISSISSIPPI RIVER. 
During the months of July and August, 1920, the Bureau of 
Fisheries made a study and appraisal of the mussel resources in a 
portion of the upper Mississippi River, beginning at a point about 
5 miles above Red Wing, Minn., and extending down through Lake 
Pepin, a distance of about 80 miles, to Lamoille, Minn. The work 
was undertaken with reference to recent administrative action on 
the part of the States of Wisconsin and Minnesota providing for 
the closure .of certain areas for the protection of the fresh-water 
mussels while permitting the fishery to continue in alternate open 
areas. The data acquired in this investigation are expected to estab- 
lish a basis for comparison of conditions before and after a period 
of protection. The investigation was conducted under the Fair- 
port biological station by Dr. N. M. Grier, with two assistants. Ob- 
servations were made in five open and five closed areas. 
Many data were secured regarding the depletion of formerly pro- 
ductive areas of mussel fishery, the diminution in abundance of 
mussels in different beds being attributed variously to the indirect 
effects of the construction of wing dams as aids to navigation, to 
excessive fishery, and perhaps in some cases to the dumping of rub- 
bish in the river in the vicinity of cities. 
The information gained will serve also as ay aid to the Bureau 
in the conduct of mussel propagation for the rehabilitation of de- 
pleted and protected areas. 
EXPERIMENTS RELATING TO MUSSEL PROPAGATION. 
Experiments in retaining in inclosures fish artificially infected 
with glochidia of the Lake Pepin mucket, Lampsilis luteola, have 
been continued in Lake Pepin by Roy S. Corwin, scientific assistant. 
It was found in certain experiments that pike perch infected as late 
as August 19 carried glochidia until the following May, and that 
mussels during the second year of growth will thrive in an inclosure 
with a density of 18 mussels to the square foot. Third-year mussels 
with eight to the square foot flourished and showed an average in- 
crease in length of more than 100 per cent in one year. 
Artificial infections of the Lake Pepin mucket on pike perch re- 
tained in a fine-meshed inclosure in the lake yielded an average of 
833 juvenile mussels per fish. Assuming that these fish bore the 
usual infection of about 3,000 glochidia per fish, the yield of young 
mussels was 27.4 per cent. This is a much higher percentage than 
has ever been assumed to result from practical operations in artifi- 
cial propagation of mussels. 
Dr. L. B. Arey continued his study of the encystment of the 
glochidia of the fresh-water mussel. It has been established that 
the tactile response of the glochidium alone is adequate to insure 
attachment. The view that glochidia regularly attached to the host 
through a chemica! activation by blood, derived from gill hemor- 
rhages, appears to be untenable. Cyst formation is not initiated or 
controlled by any vital influence of the glochidium. It has been 
induced by the application of tiny metallic clips to a gill filament. 
