U NORTHERN FISHES 



or in the case of some species, such as walleyes, the eggs may be placed 

 in large jars into which run constant streams of water, keeping the eggs 

 agitated. 



After fertilization trout and whitefish eggs can be maintained on ice 

 for weeks before hatching. The eggs of these species must be kept and 

 hatched in the dark because light seems to be fatal. Cold water is also 

 necessary. Their period of development is slow and they usually take 

 several months to hatch. Warm-water fishes usually hatch in one to 

 two weeks. The newly hatched fry are commonly inactive for several 

 days and feed by absorbing food from the yolk sac which is still at- 

 tached to them. x\fter several days they start searching for food. Their 

 first food is the minute aquatic animals, mostly water fleas (Daphnia) , 

 which are common in the shallow water of lakes. Since this type of 

 food is not always easy to supply in the hatchery, the fry may start 

 feeding on each other. Consequently, it has been common practice to 

 plant the fry in natural waters as soon as possible after hatching. 



Since most fishes produce enormous numbers of eggs, it is possible 

 to secure many millions of eggs from a relatively few fish. The success 

 of the artificial hatch depends on many factors and the percentage of 

 eggs hatched may vary from 10 to 90 per cent. Nevertheless, with such 

 enormous numbers of eggs, the number hatched frequently runs into 

 many millions. "When the newly hatched fry are transported from the 

 hatchery to the lake, thousands can be placed in a ten-gallon can, so 

 that the cost of transportation is much less, than for larger fish. 



When planted in lakes the rather helpless fry are subject to many 

 hazards. Sudden temperature changes are fatal. Many enemies await 

 them and thousands, if not all, are killed by predators ranging from 

 tiny water bugs to small perch. 



In order to avoid these potential losses at planting time, a plan has 

 been developed for rearing them to fingerling size. The fry are placed 

 in small rearing ponds which should be free from any predators, and 

 the ponds are treated with fertilizer to provide an abundance of 

 natural food. Sucker fry and later minnows are provided to furnish 

 food after the first two weeks. 



In the fall the ponds are drained and the fingerlings are removed 

 and planted in lakes. Because of their size, natural losses, and the ex- 

 pense of rearing and transportation, only thousands instead of mil- 

 lions can be produced by this method. But stocking with fingerlings is 

 popular in many places because these fish are too large to be con- 

 sumed by perch and other small predators prevalent around the 

 margins of lakes. 



Nest-building fishes, such as bass, crappies. and sunfishes, have re- 

 fused to accommodate themselves to methods of stripping and insist 

 on retaining their natural methods of reproduction, which involve a 



