MANUAL OF FISH-CULTURE. 113 



pan of water. This will deadeu the fall of the eggs from one tray to 

 the other and i'ree what few adhere to the first tray. 



In a Avater teuipertiture of from 40° to 45° F., hatching will begin iu 

 from 75 to 90 days. The dark hue of the egg as a whole, the distinct 

 outline of the fish, and its convulsive movements show the apj)roach 

 of the hatching period. If the weather is clear and cold these indica- 

 tions may continue for some time, but with the advent of a single warm 

 day more than 50 per cent of the fry are ajit to break their shells. 



As the total number of eggs received at the hatchery has decreased, 

 in order to determine the number of fry that will be hatched they are 

 now measured again by first emptying the eggs in the large i)an 

 described above, and then placing 4,000 each upon trays, in this case 

 made of wire cloth with a i^-inch mesh. Should the temperature 

 remain uniform the hatching will cover a number of days, but a sudden 

 rise or fall in the tem'perature will have a marked efl'ect in either 

 advancing or retarding the further develoi)meut of the eggs. 



The dead shells from the hatching fish must be removed or they 

 will clog the trays and stop the circulation of water. To provide 

 against this, one box of trays is emptied into a j)an of water and the 

 eggs stirred with a feather; the shells rise to the top and can be easily 

 poured off, and by repeating this operation several times the hatching 

 fish are entirely freed from this refuse. In returning the fish and eggs 

 to the trays they should be divided as equally as possible among the 

 ten trays. The necessity for this depends on the rapidity of hatching 

 and perhai^s a single box need be served in this manner only three 

 or four times during the hatching i)eriod. 



The care of the fry from this time to their distribution, if distributed 

 before the absorption of the food-sac, is somewhat similar to the treat- 

 ment described for eggs. Monstrosities, " blue-sacs," and dead fry are 

 picked out as soon as they are discovered. The yolk-sac attached to 

 the fry will be gradually absorbed and the fry so increase in size that 

 4,000 overcrowd one tray, and when the sac is about half gone, which 

 is in about three or four weeks after the fish are hatched, it is necessary 

 to reduce the number upon each tray to li,000. 



DISTRIBUTION OF THE FRY. 



Lake trout should either be planted while the food-sac is still visiMe, 

 or not until they possess the vitality of the yearling. Trout planted 

 when the food- sac is within one or two weeks of complete absorption 

 have suflicient nourishment to sustain life until they are acclimated to 

 their surroundings, as well as the natural impulse from the beginning to 

 take the minute particles of food which they find. As from 2,000,000 to 

 4,00(>,000 lake trout are hatched at Northville annually, it is impossible, 

 with the present facilities, to hold them all in rearingtroughs and ponds 

 until they become yearlings, and the fry are usually distributed direct 

 from the hatching-boxes. 



1<". C. K. 1897 8 



