164 BULLETIN OF THE BUREAU OF FISHERIES. 



bottom (chiefly used in ponds) ; (3) the bottom crate; (4) pen with wooden or box bottom; 

 (5) concrete ponds; (6) earth ponds; (7) troughs of sheet metal, wood, or concrete tanks, 

 and aquaria. 



(i) The floating crate with closed bottom was devised to meet the special conditions 

 of a large river where the level is subject to considerable change, where excessive turbidity 

 frequently prevails, and where there is a decided current. To prevent the washing away 

 of the microscopic mussels, while permitting the passage of water and food through the 

 crate, the crates are constructed of fine-meshed (100 mesh to the inch) wire cloth on a 

 wooden frame. The form of the crates and the maimer of using them may be under- 

 stood from the illustrations (PI. XIX, figs, i and 2). They are described in more detail 

 in a forthcoming paper by A. D. Howard. A plant of young mussels is obtained by 

 placing infected fish in the crate and removing them after they are freed of the mussels. 

 The results with the floating crate have been quite satisfactory with the Lake Pepin 

 mucket, and a few yellow sand-shells have also been obtained in them. Other river 

 mussels have failed to develop beyond early stages. Good results with river mussels 

 would be expected, but it is found that even with the crate floating in the river, the 

 conditions within it are not those of the natural habitat of the mussel on the clean 

 current-swept bottom of the river. No one has yet devised a container to employ under 

 such conditions that would fully answer the requirements. 



(2) The floating crate with open bottom has been used in artificial earth ponds. 

 The bottom is actually closed to fish, though open to juvenile mussels, since it is made of 

 coarse-mesh wire cloth (i ^-inch mesh). The infected fish are kept inclosed until freed of 

 glochidia, which fall through the wire to the bottom of the pond. To obtain the mussels 

 when developed, the water is temporarily drawn from the pond. Good results have 

 been obtained with the Lake Pepin mucket only. 



(3) The bottom crate has been used in studies of growth of larger mussels, by 

 Lefevre and Curtis (1912, p. 180), Coker, and others, and in experiments in pearl culture 

 by Herrick (Coker, 1913). It has recently been adapted for the purpose of retaining 

 infected fish and securing plants of early postparasitic stages of mussels. The crate 

 rests on the bottom of the pond. It may have either a solid bottom or one of screen 

 wire which, of course, sinks a little way into the mud covering the bottom of the pond. 



(4) The pen of galvanized netting with wooden floor is adapted to quiet water 

 without current. The pen, having walls of wire cloth that extend from the bottom to a 

 safe distance above the surface of the water, allows the fish to seek their own range of 

 depth and permits the mussels that fall from the fish to remain close to the bottom of the 

 pond or lake, as is natural for them. The mussels are collected by raising the wooden 

 bottom at the end of the growing season. Excellent results have been obtained in Lake 

 Pepin with the Lake Pepin mucket. In the most successful experiment more than 

 11,000 living young were secured in one crop in a pen 12 feet square. These were 

 liberated from 79 fish which had been artificially infected (Corwin, 1920). 



(5) Concrete ponds having vertical sides have been planted in the usual way and 

 the fish removed with a seine after the mussels have been shed. Some 50 examples 

 erf a river-inhabiting species, the pimple-back, Quadnda pustulosa, were reared to the 

 age of 4 years in one experiment, but other trials with this species have failed. The 

 usual consistent results have been secured with the Lake Pepin mucket. 



(6) Earth ponds with devices for control of depth and water supply have been 

 stocked with mussels by introducing infected fish. As a rule the fish are not removed 



