FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 717 



It consists of a series of ordinary milk pans held in a frame, one above another, 

 in numbers to suit conditions, the bottoms of the pans perforated with a nail or 

 other pointed instrument which will leave a ragged edge to each perforation on 

 the underside of the pan. 



This apparatus is set up at the head of the trough in such position that the 

 supply pipe empties into the topmost pan, and the water must pass through 

 the series before reaching the trough. By this separation into fine streams the 

 water is thoroughly exposed to the air, thus rectifying any abnormality of air 

 content. 



At nearly all trout hatcheries it has been customary to place horizontally 

 below the supply pipe at the head of each trough a screen consisting of a light 

 frame, bottomed with wire cloth or perforated metal. This is designed not only 

 to break the force of the stream entering the trough but to aerate or deaerate 

 the water and at the same time catch foreign substances and animal life — the 

 latter at times being quite objectionable. Such screens, however, have almost 

 invariably caused the water to spatter over the sides of the trough, resulting in 

 constantly wet surroundings. To overcome this objectionable feature a conical 

 perforated screen has been devised by Mr. M. E. Merrill, of the St. Johnsbury, 

 Vt., station. When the screen is in place the current of water falls directly 

 on the apex of the cone, and thus is spread over the entire perforated surface, 

 accomplishing the objects of all other styles of head screens, and avoiding the 

 spattering of water over the sides. 



A device for assorting young salmon and trout was introduced in the 

 Bureau's operations by Mr. J. P. Snyder, an employee at one of the stations. 

 It consists of a series of screens by means of which to separate the fingerlings 

 into sizes. 



In length the screens are slightly less than the width of the troughs, to 

 facilitate sliding them along. There should be two screens for each size of 

 mesh. In use one screen is carefully inserted at the foot of the trough close to 

 the tail screen, due precaution being taken that no fish are pinched and that 

 none are left between the foot screens and the end of the trough; midway of 

 the trough a screen should be securely fastened in a vertical position by wedging. 

 After the first screen is in position a similar one is inserted at the head of the 

 trough and then moved along toward the center. 



As the two screens are brought closer together the fish between them 

 become frightened, and all that are small enough escape through the mesh of 

 the screens. The distance of the second screen from the first should depend 

 upon the number and size of the fish in the troughs, and also upon the number 

 that escape through the screen. The second screen should also be fastened by 

 wedging. Then the hand of the attendant is moved about among the fish 

 between the screens to guard against any small ones finding a hiding place. In 



