ARTIFICIAL PROPAGATION OF TROUT. 37 



fish of the rainbow trout were affected by an alum solution below 

 a strength of 1 part of alum to 8,000 parts of water. Rainbow trout 

 2 inches long were held in a 1 to 20,000 solution for a period of two 

 weeks without apparent harm. 



SPAWNING PONDS. 



In constructing ponds one of the first considerations is to place 

 the fish absolutely under control, that they may be handled without 

 delay or inconvenience. The ponds at Wytheville formerly were 

 constructed of wood, but when they were rebuilt recently concrete 

 was used. They are 15 by 50 feet and 3 feet 4 inches to 3 feet 6 

 inches deep, shaped as shown in Figure 11, page 38, and have 

 proven very satisfactory. The length of the ponds may be in- 

 creased up to 100 feet without impairing their efficiency, though 

 the width should not exceed 12 to 15 feet. Much depends upon the 

 volume of water available, but ponds more than 100 feet in length 

 are difficult to clean and care for. Excellent water circulation is 

 obtained in all parts, there being no corners in which refuse can 

 lodge. From the outlet the bottom has a gradual rise of 6 inches 

 in its entire length, making it practically self -cleaning. Most of 

 the refuse will pass off, and any remaining can be disposed of read- 

 ily by lowering the water level for a short period and then flushing 

 the pond with fresh water. This method obviates the necessity of 

 handling the fish, an important point, especially at the approach of 

 the spawning season. 



A guard rack made of thin narrow slats is arranged on an incline 

 of about 45°, as shown at A, Figure 11. If the water is to be used 

 again in ponds below, a " receiver " is built underneath the bottom 

 of the pond, at the lower end, between the foot of the guard rack and 

 the dam boards, and the floor of the pond immediately over the 

 receiver is cut away and fitted with a grating. This allows all waste 

 to fall through into the receiver. From there it is washed through 

 the sluiceway by opening the gate valve. The sluiceway, Z>, is of 

 8-inch terra-cotta pipe and connects with a 12-inch drain of the 

 same material. 



The pond is provided with a spawning race about 14 inches deep, 

 4 feet wide, and 25 feet long, placed at the upper end of the pond, 

 as shown in Figure 11. Three division boards (shown at E), about 

 12 feet long and of suitable width to come within 1 or 2 inches of the 

 surface of the water when the pond is filled, are firmly fixed at the 

 bottom. The object of these boards is to form four entrances to the 

 raceway, so that one or two pugnacious fish can not command the 

 approach and keep back spawning fish inclined to enter. There is 

 a dam across the raceway about 4 inches high for the purpose of 

 bringing the water to that depth in the lower end, so that when 

 trout enter the raceway they will find sufficient water in which to 

 swim freely and not be inclined through fear to return to the pond. 



At the approach of the spawning season the water level of the 

 pond is raised to within 6 inches of the top of the dam in the race- 

 way, which will give the fish in entering the raceway a jumj) of 7 

 inches, allowing 1 inch for the depth of water on the dam in the 

 raceway. This distance has been found the most satisfactory, as 

 under such conditions only spawning fish will ascend. If a jump 



