804 BULLETIN OF THE BUREAU OF FISHERIES. 



degree that becomes dangerous to the fish, and a thorough cleaning out 

 becomes necessary. This is effected in the following manner: 



The drains are opened and the water, the surface of which usually is at level 

 o, is allowed to run out till it reaches level b. (Fig. 3.) The pond is then, by 

 the watertight bulkhead, divided into two compartments, D and E, and with 

 a number of fish in each compartment. Supposing D is to be cleaned first, 

 the water in E, under continual renewal, is kept level with the top of the 

 bulkhead, while it is lowered still more in compartment D, until about 

 I foot above the flooring. The fish are then caught with dip nets and lifted 

 over the bulkhead into E. After this is done, all the water is let out from D, 

 and the place scrubbed and washed thoroughly. To facilitate the work, the 

 middle part of the flooring ought to be made like a hatch to be lifted oft", as 

 cleaning underneath is necessary. 



After cleaning, compartment D is filled again, the fish lifted in, and E 

 cleaned out in the same manner. How often this is to be repeated depends 

 on the number of fish in the pond, the nature of the food, and on the specific 

 gravity and temperature of the water. I have never had occasion to do it 

 more than three times in the season; usually once or twice. 



The spawning. — With the exception of the necessary handling when 

 cleaning the pond, the spawners need not be touched during the whole season. 

 If properly fed, and with a constant renewal of the water, they soon will become 

 accustomed to their prison life, and in a short time be so tame that they will 

 take food out of the hand. Consequently the fish will thrive well, and the 

 development of the reproductive organs, as well as the spawning, will proceed 

 in the ordinary manner, just as if the fish were living under natural conditions. 



The pond, however, has one great advantage. All the eggs are sure to be 

 impregnated, as the whole volume of water, practically speaking, is filled with 

 sperm, a result of the great number of spawners crowded together in a narrow 

 space. 



The cod generally spawn in the evening between 8 and 11 o'clock, and, 

 provided the water has a specific gravity of 1.021 or more, the eggs will float 

 up and form a thin layer on the surface of the pond. 



Collection of the eggs.- — I have mentioned above that the pond receives 

 from 30,000 to 50,000 liters of water per hour. The outlet is shown at d 

 (fig. 2) , and is formed as a depression or cut in the front wall, 3 feet wide and 

 1)4 feet deep. Its continuation is a wooden chute e of the same dimensions 

 leading into a receiver / somewhat broader and deeper than the chute. From 

 this the outflow is through an iron pipe g, placed so that its upper end regulates 

 the height of the water in the pond. (See also fig. 4 and 5.) 



In the receiver / the egg collector (fig. i, pi. ci) is placed in such a manner 

 that its open end fits exactly to the open end of the chute. The bottom and 



