14 U. S. BUREAU OF FISHERIES. 



recovered. These mussels spent their parasitic life on wall-eyed pike 

 and saugers and represent an 84.6 per cent survival of the glochidia, 

 constituting the total experimental infection. The production of 

 these juveniles averaged 237 per square foot of bottom surface. The 

 mortality of mussels after having reached this length is approxi- 

 mately nil. 



The results of these experiments stand as an indication of the pos- 

 sible usefulness of controlled methods over the present method of 

 artificial propagation in which infected fish are liberated in natural 

 bodies of water to drop the juvenile mussels on bottoms, where 

 it is unlikely that more than a 2 or 3 per cent survival results. These 

 results are particularly significant if, based on the apparatus used, 

 artificial mussel propagation may be carried on more efi'ectively than 

 formerly with results more tangible, cheaper, and less limited by 

 natural physical, chemical, and biological factors. 



During the year two undescribed parasites of fresh-water mussels, 

 ciliates of the genus Conchophthirius have been observed. One of 

 these has no particular significance as it is apparently harmless. The 

 other, however, evidently is the cause of the mortality of large num- 

 bers of larval mussels while they are still held in the marsupia of 

 the adults. Mussels seriously infected have been taken in Lake 

 Pepin and from the ponds at Fairport. 



Statistical and biological surveys of mussel beds have been carried 

 on during the year at Lake Pepin and at Lake Pokegama, Minn. 

 Artificial culture of mussels by the inoculation of the host fishes has 

 been carried on for several years in both bodies of water. At Lake 

 Pepin there has also been in operation for some time a five-year alter- 

 nate sectional closure of the lake to commercial mussel fisheries. 

 The surveys, therefore, especially in the case of Lake Pepin, have 

 provided important data regarding the benefits derived from arti- 

 ficial mussel culture and the advantages to be expected from pro- 

 tective closure of streams. The survey of Lake Pepin indicates, 

 though not conclusively, that the important commercial mucket 

 (Lampsilis luteola) has increased in the lake. This apparently is 

 due to the artificial culture of this species that has been carried on 

 by the bureau since 1913. The noncommercial species and other 

 commercial species that have not been propagated apparently have 

 decreased during the same period of time. 



The presence in the lake of a large number of mussels under 10 

 yt>.ars old further corroborates the value of the work. The returns 

 from this survey are the best indication of the value of artificial 

 mussel culture so far obtained. The protective closure, as inaugu- 

 riited in 1918 through the cooperation of the States of Minnesota and 

 Wisconsin, is unquestionably a desirable aid in perpetuating the 

 mussel fisheries of the country. 



Physiological and anatomical studies of the mussel embryo and its 

 irl^relopment, and experimental efforts at metamorphosis induced 

 v^'jthout the normal stage of parasitism on fishes, were conducted by 

 Dr. Edgar Allen at the fisheries biological station, Fairport, Iowa. 

 ObesFvations were made on a number of mussels, but particularly on 

 the species Anodonta irtibecillis and /Strophitus edentulus. 



Dr. L. B. Arey continued his investigations of (1) the history and 

 structure of the normal cyst of fish tissue surrounding the mussel 

 glochidium, its relations to the surrounding host tissues, mutual 



