4 U. S. BUREAU OF FISHERIES. 



but as yet this method has not been perfected to such an extent that 

 it is commercially practicable. Further experiments with a new 

 method of artificially propagating the oyster were conducted by the 

 U. S. Bureau of Fisheries at Milford, Conn., during the summer of 

 1923, the results of which will be described in the following work. 



OBJECT AND SCOPE OF THE INVESTIGATION. 



The various reasons for imdertaking experiments in artificial 

 propagation are, first, to determine a reliable method for obtaining 

 healthy, vigorous spawn in quantities; second, to devise a means for 

 rearing the free-swimming oyster larvae until they reach the setting 

 stage; third, to make more extensive studies of the oyster larvae 

 under controlled conditions in regard to embryonic development, 

 habits, food, and most favorable environmental conditions; fourth, 

 to produce larvae for tests in regard to the effect upon them of vari- 

 ous chemicals in solution; fifth, to try out new materials for col- 

 lecting and handling " set " ; and sixth, to determine from the re- 

 sults obtained the possibilities of making artificial propagation suc- 

 cessful on a practical comnitTcial scale. 



The many steps involved in artificially propagating oysters con- 

 sist briefly of (1) obtaining natural spawn from the adults, (2) rear- 

 ing the larvae during the long free-swimming period, (3) placing 

 suitable collectors in the water at the proper time for the attach- 

 ment or " setting" of the larvaa, and (4) transferring the young at- 

 tached oysters or '' spat " to protected beds where conditions are 

 most favorable for growth and development. 



EQUIPMENT USED IN THE INVESTIGATION. 



Careful observations of salt-water aquaria have indicated that, in 

 general, metallic apparatus is unsuitable if a pure and natural water 

 supply is to be maintained. The corroding action of the sea water 

 upon brass, copper, galvanized iron, etc., renders them unfit as recep- 

 tacles for the storage and conveyance of salt water. For this reason 

 the equipment used in this investigation was constructed of wood, 

 hard rubber, and glass when possible, in order that nearly natural 

 conditions might be produced. The apparatus used consisted of one 

 cylindrical 500-gallon wooden storage tank, one rectangular 100- 

 gallon wooden spawning tank with trays, four rectangular 25- 

 gallon rearing tanks, two small cylindrical rearing tanks, an air- 

 compressor, rotary water pumps, glass pipe, and hard rubber and 

 wood faucets. The problems of filtration were solved to a great 

 extent by the use of a new material known as " filtros." It is a 

 white, rigid, porous, artificial stone, composed essentially of silica, 

 and is similar to a sand filter in block form. The various grades of 

 uniform porosity in which it is made make it suitable for retaining 

 materials or organisms of any definite size and still allow a good 

 flow of water. The filtros blocks used in the experiments were 12 

 inches square and 1| inches thick and were fitted into grooves in 

 the rearing tanks as'' shown in Figure 1. Blocks of various densi- 

 ties were used in accordance with the growth and size of the larvae, 

 and after being in use for five or six days were easily cleaned with 



