18 U. S. BUREAU OF FISHEIIIES. 



Tho trays more generally used consist of frames 16 inches long by 

 14 inches Avicle, made of pine strips 1 inch by | inch. To these frames 

 galvanized wire cloth of an oblong mesh is fastened. The cloth is 

 usually woNen S tlir(>ads to the inch, Avith a mesh seven-eighths inch 

 long, gal\'aniz(Hl after weaving, although it is gauged to retain the 

 eggs and ])ciinit the newly liatched fry to fall through. 



Wiiile the basket method was devised to meet adverse conditions 

 at some of the Federal iish hatcheries and at such stations is con- 

 sidered to have meritorious features commending it for general 

 adoption, many tish-culturists prefer the tray system, while still 

 otiiers us(> from choice the C^lark hatching box, which insures a good 

 water eii'eulation. J*erhiips the most compact and economical 

 method is I'ounil in the AVilliamson trough, which has comi)artments 

 divided l)y galvanized iron })artitions as described in this article. 

 From 8 to 14 trays are placed in each compartment, according to 

 the depth of the trough. The How of water is always up through 

 the stack of eggs, which are held down in the compartment by a 

 crossbai- or binder. To facilitate their removal from the trough, a 

 strap uvmIv of 2S-gauge galvanized iron and having Avooden handles 

 on each end is piaci'd around the stack ot trays. This also serves to 

 liold the trays togetlier and })revents the escape of the fry, which 

 W(Mdd occur if the trays were lifted out singly. The troughs de- 

 scribed in the section on rainbow trout, with trays 28 inches long, 

 may be very successfully used in brook-trout culture. The eggs on 

 sucli trays are always under the innnediate observation of the lish- 

 culturist, and dead eggs are easily discernible.* 



FIELD OPERATIONS.^ 



While a very largo percentage of the brook-trout eggs handled in 

 Iish culture is obtained from tlomi'st icated Iish, the bureau still op- 

 erates a number of prolitable liekl stations where eggs are obtained 

 from wild Iish. Where natural spawning on a sulliciently large 

 scale to make the gathering of wild eggs prolitable occurs within 

 reasonable distance of a hatchery, it is customary to establish tem- 

 porary stations in the innnediate vicinity of the spawning grouiuls. 

 After taking and developing the eggs to a point where they will bear 

 transportation they are shipi)ed to the central station to be hatched. 

 In certain instances green eggs may be shipped for a consiilerable 

 distance without serious loss, though whenever practicable it is de- 

 sirable to deveh)p them to the eyed stage before subjecting them to a 

 long journey, l^rook trout work of this character is extensively 

 conducted in Colorado, Utah, Wyoming, and Vermont. 



If lakes or ponds constitute the spaAvning grounds, their bottoms 

 must be cleared for seining operations. AVhere the lakes are arti- 

 ficial and retaining dams have been built, the water usually may be 

 draAvn and the Iish collected easily. HoAvever, this process may in- 

 volve the carrying away of most of the natural food contained in the 



« Artificial Propagation of Whltoflsh, Lake l>out, and GraylinR. By O. C. Leach, 

 assistjiut In cliarsv of llsli iiilturo. Api^emllx III to tho Rcixirt of U. S. Commissioner 

 of I'Mshorlcs for IS)-."*. lUircaii of Fishorios DocuuuMit iMt). 



'■Notes on tho onptiuv of wild brook trout and coUoctlon of their eRKs were coutrllnitcd 

 by A. H. Dlnsiuoro, superintondeut of the St. Johusbury (Vt.1 station of the nuroau of 

 t^sherles. 



