126 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table io. — Average Length of Six Examples op the Lake Pepin Mucket, Lampsilis'luthola, 



Reared in Pond jD at Fairport, Iowa. 



Time of measurement. 



Length. 



Close of second growing season. 

 Close of third growing season •*. . 

 Close of fourth growing season . . 



Close of fifth growing season 



Close of sixth growing season . . . 



a The records of the original lot for the third year having been lost in the fire, there is substituted a corresponding record for 

 the third year of mussels of another lot recorded in Pond 8D. The mussels in Pond 3D were from a fall infection and those in 

 8D from a spring infection; therefore the former are sUghtly older. 



Another species of pocketbook, Lampsilis (Proplera) capax, had attained a length 

 of 49 mm. (1.93 inches) at the end of the second season, indicating a slightly more 

 rapid growth for this species than for Lampsilis ventricosa. Thinner-shelled species of 

 the genus Lampsilis may grow more rapidly. Thus some examples of the paper-shell 

 Lampsilis (Proptera) IcEvissima, known to be not over 1 6 months of age (in free life) , 

 had attained lengths of 78 to 81 mm. (over 3 inches). An example of the paper-shell, 

 Lampsilis (Paraptera) gracilis, grew from 17.6 mm. (0.7 inch) to 107 mm. (4.2 inches) 

 in 2 years 9 months and 18 days, the rate of growth averaging about ij4 inches per 

 year. 



The very thin-shelled mussels of the genus Anodonta grow even more rapidly. 

 Examples of the floater or slop-bucket, Anodonta corpulenta, taken from a pond at the 

 Fairport station 16 months after the ponds were constructed, varied in length from 

 66 to 88 mm. (2.59 to 3.46 inches). Examples of another paper-shell, Anodonta sub- 

 orbiculata, taken at the same time from another pond of the same age, but which may have 

 offered less favorable conditions, were 64 to 67 mm. in length (2.52 to 2.63 inches). 



With regard to heavy-shelled mussels, such as the niggerhead, pimple-back, and 

 blue-point, there is much less satisfactory evidence as to growth. They undoubtedly grow 

 much more slowly than mussels possessing thin shells, yet the rates of growth secured 

 in such experiments as have been conducted can hardly be assumed to be representative 

 of the conditions prevailing in nature. The species are not well adapted to life in tanks 

 or ponds, and there are few places where measured specimens can be placed in rivers 

 with any assurance that they will remain undisturbed or may be recovered at a later 

 time. In Lefevre and Curtis's experiments (191 2) an example of the hickory-nut, 

 Obovaria ellipsis, that was practically full-grown when first measured, gained 5 mm. (one- 

 fifth of an inch, 0.197) ^^ ^ little less than 2^ years. In the same period an example 

 of Quadrula solida, somewhat less mature, gained 10 mm. (two-fifths of an inch, 0.394). 



In the follownng table (11) there are indicated sizes, at the close of the second year, 

 of certain mussels reared accidentally or intentionally in ponds at the Fairport station. 

 The short-term breeders, at least, were a little less than lyi years of age. 



Since these are all mussels of river habit, it can not be assumed that the growth 

 attained in ponds is representative of the rate of growth in a natural environment. 



