ANNUAL GROWTH OF FRESH- WATER MUSSELS 1 
By Thomas K. Chamberlain, Associate Aquatic Biologist 
CONTENTS 
Introduction 
Method 
Material 
Individual species 
Yellow sand shell 
Length in relation to age 
Weight in relation to age 
Thickness in relation to age 
Page 
713 
713 
716 
716 
716 
717 
725 
728 
Individual species — Continued. 
Lake Pepin mucket 
Buckhorn and Pope’s purple 
Area of shell 
Discussion 
Summary 
Bibliography 
Page 
730 
734 
736 
736 
737 
738 
INTRODUCTION 
In view of the progressive depletion of the natural beds of commercial fresh- 
water mussels used in the manufacture of pearl buttons, it has become desirable to 
determine the action of various factors bearing on future supplies of these shells. 
At present no adequate data exist on the age and growth of commercial mussels; 
and, consequently, little is known concerning the age at which these mussels could 
best be taken from the streams, considering both the economic value of the shells to 
the manufacturers and the interests of conservation. Accordingly a detailed study 
of the growth of fresh-water mussels representing four commercial North American 
species has been made, using the “annual ring” method as applied to mollusks by 
Weymouth (1923) in his work on the Pismo clam. 
The determinations of the length-age relations of the upper Mississippi shells 
used in these studies were begun in the laboratories of physiology at Stanford Uni- 
versity in 1926. Subsequently, additional material was measured at the United 
States Bureau of Fisheries Biological Station, at F airport, Iowa. The length-age 
and weight-age studies of the Arkansas and Texas shells, and all of the thickness-age 
studies, were made in the laboratories of physiology of the University of Missouri. 
The writer is greatly indebted to Dr. F. W. Weymouth, of Stanford University, and 
to Dr. M. M. Ellis, of the University of Missouri, for their advice and suggestions 
in connection with this work. 
METHOD 
In many organisms the variations in growth rate, occurring at intervals and 
associated with such factors as temperature or drought, produce rings or other marks 
in the hard structures. The use of these records in the determination of the age of 
trees, where the rapid growth of summer, the slow growth of winter, and sometimes 
intermediate stages caused by drought or other unfavorable conditions, leave dis- 
tinct rings in the cross section of the trunk, which can be recognized as belonging to 
1 Approved for publication, Sept. 30, 1930. 
713 
