480 



U. S. BUEEAU OF FISHERIES 



center section of the table to receive the fry — and into which the 

 discharge water from each jar enters. The fry tanks in general use 

 are of glass, though wooden tanks are entu-eiy satisfactory. A 

 1 J/^-incn iron pipe, connected with the main water supply, is extended 

 lengthwise over the center of each table. In tliis pipe, on either side, 

 are inserted 3'^-inch brass pet cocks, one for each jar, from which 

 water is supplied to the jars tlirough ^-inch rubber tubing. The 

 overflow from the fry tanks is taken care of by a standpipe, 1 yi 

 inches in diameter, running through the bottom of the tank and 

 secured by a lock nut. Inside the tank the pipe is entirely suiTounded 

 by a frame, either square or circular, covered with wire gauze, which 

 excludes the fry from the overflow. At one end of the table a pipe 

 of suitable size is fastened to convey 

 waste water to the drainage system. 



In view of the comparatively short 

 incubation period of shad eggs and certain 

 other considerations, shad-hatcliing oper- 

 ations have been conducted on the type 

 of table herein described. Should it be- 

 come expedient, because of an increased 

 number of eggs, to curtail space in the 

 hatchery or to conserve the water sup- 

 ply, the simpler forms of the "single 

 battery" used in pike-perch work could 

 be used successfully for shad. 



HATCHING JARS 



Fig. 6. — McDonald automatic hatch- 

 ing jar 



Very early in the development of its 

 fish-cultural activities the Bureau of Fish- 

 eries was confronted with the necessity 

 of dealing with the eggs of shad, white- 

 fish, and other species in immense num- 

 bers. If the work was to be of practical 

 value, eggs by the hundreds of millions, 

 not by thousands, must be handled. 

 After successive experiments the McDon- 

 ald automatic hatching jar Vv^as devised, and it is still in favor with 

 many fish-culturists. The Chase and Downing jars, which are also 

 in general use, are simplified modifications of the McDonald jar. 



Perhaps the most meritorious feature of these jars is that they 

 prevent the development of the saprolegnious fungus, which caused 

 so ^reat a mortaUty in some other forms of hatching contrivances in 

 which all the ova were not in continual movement. The very gradual, 

 gentle, and continual rolling movement of the ova upon each other 

 in the jars apparently prevents the spores of the fungus from adher- 

 ing. The cleanliness of the apparatus is also advantageous, and as 

 the material of which they are made is glass the progress of develop- 

 ment can be watched satisfactorily from the outside of the jars. 



McDonald jar. — This jar (lig. 6) is a cylmdrical glass vessel of about 

 7 quarts capacity, with hemispherical Bottom, supported upon three 

 glass le<Ts. The top is made with threads to receive a screw cap. It is 

 closed by a metallic disk, perforated with two holes % inch in 

 diameter — one in the center admits the glass tube that introduces 



