MANUAL OF FISH-CULTURE. 77 



males are very pugnacious at this season, and sometimes fight for an 

 hour or more at a time, until they are entirely exhausted; they run at 

 each other with open mouths, lock their jaws together, and in that 

 position sink to the bottom of the pond, where they lie for a short time, 

 each holding the other in his grasp until rested, when they rise and 

 resume the combat. As their teeth are abnormally long, they scar 

 each other and even bite pieces of skin and tlesh from the sides of their 

 antagonists. 



The males are good breeders at 2 years old, but very few females 

 produce eggs until the third season, when they are from 30 to 36 months 

 old. At Wytheville hatchery about 1 per cent of the females spawn at 

 3 years of age; about 50 per cent at 3 years, and about 85 per cent 

 each season after that. About 15 per cent of the fully matured females 

 are barren each season. It was at one time thought that the same 

 individuals were barren each year, but experience has shown that 

 such is not the case, as fish which were barren one season have been 

 held over, in a separate pond, until the following year, when a large 

 portion, if not all, produced eggs. This sterility may be the result of 

 injuries received during the previous season, during the progress of 

 spawning. 



EGGS. 



The number of eggs produced in a single season depends upon the 

 size and age of the fish. The maximum from one 3 years old, weighing 

 i to 1^ pounds, is from 500 to 800; from one 6 years old, weighing 2 to 4 

 pounds, it is 2,500 to 3,000. The eggs vary in size from 4^ to 5 eggs to 

 the linear inch, and are of a rich cream color when first taken, changing 

 to a pink or flesh-color before hatching. 



THE HATCHING-TROUGHS AND TRAYS. 



The eggs of rainbow trout are usually incubated on trays, placed in 

 the water in troughs of various sizes and shapes. At Wytheville the 

 troughs are set in pairs, as shown on page 78, are made of the best 

 pine lumber dressed to IJ inches thick, and are 15 feet long, 14 inches 

 wide, and 8 inches deep; 14 inches from the lower end inside is a 

 guard-screen of perforated tin or wire mesh, fastened on a frame exactly 

 fitted across the trough. Tin with perforations of j^ inch for very 

 young fry, and larger ones as the fish grow, is preferable to wire. The 

 screen is arranged to slide vertically between beveled cleats, that it 

 may be kept clean easier. A plain board 3^ inches wide is placed 4 or 

 5 inches from the lower end of the trough to serve as a dam. 



In the upper end of the trough horizontal screens (B, page 78), made 

 of perforated tin, are used. These are so constructed that they can be 

 slipped forward or raised up (as shown in the illustration) in feeding the 

 fry or cleaning the troughs, and the water falling on a small wooden 

 block in the center of the screen is thoroughly aerated before entering 

 the trough. This arrangement possesses many advantages over the old 

 method, where the screens were vertical, or nearly so, as it permits the 



