MANUAL OF FISH-CULTURE. 117 



from the direct rays. A pond of this description will accommodate 

 10,000 lake trout three or four mouths old. As they increase in size 

 this number may be dimiuislied, a great deal depending upon the 

 quality and temperature of the water. 



The temperature of the water should never be higher than 65°; 

 preferably from 48° to 58°. 



As wlien kept in rearing-troughs, the fish are now fed the amount 

 they seem to desire, being neither overfed nor starved. The liver, not 

 so finely chopped as before, is thrown in with a spoon. At the first 

 feeding the fish may be somewhat wild and scatter over the pond, but 

 after one or two days they will collect at one point and take the food 

 greedily. After four weeks' time they are fed only twice per day, and as 

 they increase in size, coarser liver is given to them. Food is thrown 

 in slowly, and no more given at one time than the fish can eat, for 

 waste matter soon becomes foul, and unless drawn off will speedily 

 cause sickness. 



In from 10 to 12 months after hatching, lake trout artificially reared 

 measure from 4 to 8 inches in length and are read»y for planting. This 

 is done in the same manner as with fry, 100 fish being placed in each 

 can for transportation. 



DISEASES. 



The diseases to which lake trout are susceptible are those common to 

 all other trout. They are caused by impure water, poor food, injuries 

 received, and the attempted cannibalism of their neighbors. The first 

 three of these causes can be guarded against, but the last is much more 

 difficult to prevent. At the first sign of cannibalism the fish must be 

 thinned out, and, if feeding well, transferred to the rearing-pond, where 

 they will have greater range for development. In fact, for any of the 

 diseases this will prove of more benefit than anything else. 



It is beneficial to treat the fry with salt twice a week by shutting 

 off the water and sprinkling salt in the trough until a weak brine is 

 formed. The fish must be watched closely, and as soon as they show 

 any signs of "turning up'' a full head of water must be turned on 

 until all the brine is washed off, after which the supply may be reduced 

 to the regular amount. A small quantity of swamp earth should be 

 scattered in the tanks about once in two weeks, merely enough to dis- 

 color the water for a few moments, and allowed to wash oft' gradually 

 with the current of the water. 



