thirds full of eggs. Within 2 min- 

 utes, if the eggs and sperm have 

 been thoroughly mixed, all eggs 

 should be fertilized, each egg hav- 

 ing been entered by one sperm only. 

 The bucket of eggs is then gently 

 immersed in clear water to permit 

 the flow of water into and around 

 the eggs so that they harden. Ex- 

 cess sperm which may adhere to the 

 eggs and encourage the growth of 

 fungus is washed from the eggs. 

 Recently a device for better washing 

 of eggs has been developed by the 

 Fish and Wildlife Service, 'xhis 

 device consists of a perforated inner 

 bucket or pail which may be re- 

 moved and set in running water to 

 wash all the surplus sperm from the 

 eggs. (See fig. 12.) 



Each pail of washed eggs is car- 

 ried into the hatchery building, 

 where the eggs are deposited in 

 trays or baskets for the incubation 

 period. 



Incubation of eggs 



When the freshly fertilized and 

 washed eggs are taken into the 

 hatchery, they are placed on trays 

 or in baskets in troughs through 

 wdiich water is circulated at all 

 times. 



The temperature of the water de- 

 termines the rate of development of 

 the salmonoid eggs and therefore 

 the number of days required for 

 hatching. The highest sustained 

 temperatures should be less than 60° 

 F. Slightly warmer waters may re- 

 sult in excessive mortalities. On the 

 other hand, prolonged ])eriods of 

 water temperatures below approxi- 

 mately 34:° F. result in a very long- 

 incubation period and often in the 

 production of abnormal frv in 



which the yolk material is not ab- 

 sorbed. In waters having an aver- 

 age temperature of 50° F., it can be 

 expected that the salmon (or trout) 

 eggs will hatch in about 50 days, and 

 that the fry will have absorbed the 

 yolk sac in about 3 weeks and will 

 then start taking food by mouth. 

 The rate of development of the eggs 

 and fry is important to the routine 

 fish-cultural operations. 



Throughout the various stages of 

 development the salmon egg is sub- 

 ject to mechanical injury. There 

 are some stages in which the egg is 

 much more susceptible than in 

 others, a condition that influences 

 hatchery procedures. Two princi- 

 pal phases of development of the 

 salmonoid egg are commonly recog- 

 nized by the fish culturist. The 

 "green" state is that period of devel- 

 opment from the fertilization and 

 water hardening of the egg to the 

 closing of the blastopore. During 

 the first 24 to 48 hours of this phase, 

 the eggs are quite resistant to me- 

 chanical injury, and it is during this 

 period that the eggs must be placed 

 on the trays or in baskets to remain 

 undisturbed until the green stage is 

 complete. Usually the eggs are so 

 placed witliin a few hours of spawn- 

 ing. The remainder of the period 

 of egg development to hatching is 

 called the ''eyed'' stage and is char- 

 acterized by the appearance of the 

 eyes of tlie embryo through the 

 shell of the egg. After all eggs are 

 eyed, they can be handled gently. 

 It is common practice in salmon 

 and trout hatcheries to shock the 

 eggs at this time to rui)ture the 

 vitelline membrane of undeveloped 

 eggs. This is done by dropping the 



28 



