80 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



These amounts are ample, and probably even half would suffice if it 

 were necessary to economize in the use of water. In rearing-ponds 

 more water is required, as the circulation is not so good and the out- 

 door exposure causes the temperature to rise. If water is plentiful, 

 double the amounts stated would be advisable for pond-culture. 



During- the last two seasons at Wytheville 80 to 85 per cent of the 

 eggs taken produced fish, of which about 70 jjer cent were raised to 

 three months old and 55 per cent to yearling fisli. The loss in eggs 

 was almost entirely due to failure in impregnation, very few being lost 

 from other causes. 



CARE OF EGGS AND FRY. 



After the eggs are placed on the trays, the only attention necessary 

 until the hatching begins is to keep them clean; the dead eggs, which 

 may be known by their turning white, must be picked out at least once 

 each day. After the eye-spot can be plainly seen it is well to run a 

 feather through the eggs for the purpose of changing their position 

 on the trays, and to disclose any foreign matter or dead eggs that 

 may be hidden underneath. Tbe greatest care should be exercised in 

 handling the eggs at any time, particularly from the first or second day 

 after collection up to the appearance of the eye- spot, and then only when 

 absolutely necessary. During this period, the eggs are very delicate, 

 and even passing a feather through them may cause a heavy loss. 



The time required for hatching depends mainly upon the temperature 

 of the water. Rainbow trout eggs will hatch in water at 50° in from 42 

 to 45 days, each degree colder taking 5 days longer, and each degree 

 warmer 5 days less; the difference increases as the temperature falls 

 and diminishes as it rises. 



After the fry hatch they require but little attention .until the umbil- 

 ical sac is absorbed and the time for feeding arrives. They are exam- 

 ined each day, and the dead fish and decayed matter removed from 

 the troughs, which are kept perfectly clean, and if possible provided 

 with a thin layer of coarse white sand on the bottom, to keep the fish 

 in healthy condition. As the fish grow they should be thinned out in 

 the troughs, from time to time, as their size may require. When they 

 first begin to feed, 12,000 to 15,000 fish to the trough are not too many; 

 but by the time they get to be 1^ to li inches long they must be divided 

 into lots of 8,000 to 10,000 to each trough ; while with fish averaging 3 

 inches in length, 3,000 to 4,000 are as many as one trough will accom- 

 modate. It is advisable to give as much room as is practicable. 



REARING-PONDS. 



Ponds for rearing trout are from 8 to 12 feet wide, and of any desired 

 length up to GO feet, which, for convenience in drawing them off and 

 in feeding the fish, is about the extreme limit. The size, shape, and 

 arrangement of the x^ouds must depend upon the ground on which 

 they are to be constructed. If practicable, it is best to build them on a 



