tlioso (lifftM-ences complioatc liatcli- 

 t'ly [)r()paiiation. The adults of one 

 s[)ecies may be diiru-ult lo \\-a\) and 

 liold to spa^Ynino•, and t he youno- of 

 another species may be dillieult to 

 rear. Differences in these and 

 other respects are found within 

 species in tlie same Avaterslied, al- 

 though the hatchei'y water supply 

 or physical characteristics may de- 

 termine the extent of deviation 

 within species. 



.Vhhou^h more detailed descrip- 

 tions of procedures and equipment 

 will be given, it is well to outline 

 briefly the essential stei)s taken to 

 propag-ate salmon at a hatchery. 

 The methods are quite similar to 

 those employed at trout hatcheries. 



The first requirement is adult 

 salmon from which eggs and sperm 

 may be secured. These brood fish 

 are trapped by placing a rack or 

 racks across a stream up which the 

 mature fish are migrating. ''Ripe'' 

 females are selected and killed, and 

 the eggs are removed from the body 

 cavity. The milt or sjDerm of males 

 is expressed onto and mixed with 

 the eggs. After a few^ minutes the 

 surplus sperm is washed from the 

 eggs and the latter are taken into 

 tlie hatchery, wdiere they are placed 

 in baskets or on stacked trays so 

 arranged in the hatchery troughs as 

 to permit circulation of water 

 among the eggs. At the end of the 

 incubation period, which varies ac- 

 cording to the water temperature 

 (50 days at 50° F.), the small fish 

 or fry emerges from the egg shell 

 with an attached umbilical or yolk 

 sac that supplies sustenance until 

 the fish is capable of taking food 



hy mouth, a])pro.\iinately '■] week- 

 later. 



When the young fish are free- 

 swimniing, they are fed in the 

 hatcheiy troughs for a time and 

 then transferred to outside rearing 

 ponds. There the fish continue to 

 receive food and grow to the ap- 

 ])i-opriate size for release. In the 

 early years of salmon culture, prac- 

 tically all young fish were released 

 as unfed fry. In ij^cent years, as 

 many have been held for pond rear- 

 ing as facilities wall permit. Ex- 

 ceptions to this are the chum and 

 pink fry, which, under natural con- 

 ditions, immediately seek salt water 

 and so are released from the hatch- 

 ery. Many of the fall chinook 

 salmon also are released as fry or 

 after a few^ weeks of rearing, prin- 

 cipally because of a lack of rearing 

 space. On the other hand, wdiere it 

 is possible to do so, red, silver, 

 spring chinook, and steelhead trout 

 are held in rearing ponds for a year 

 or more. 



Some comments regarding the in- 

 dividual species of salmon and of 

 steelhead trout are of interest and 

 pertinent to a discussion of salmon 

 culture but need not be included in 

 the detailed descriptions that fol- 

 low. 



As has been mentioned, the chi- 

 nook-salmon runs into the rivers are 

 quite arbitrarily divided into two 

 groups. The spring chinook adults 

 enter the rivers in the spring and 

 early summer and usually ascend 

 the rivers farthest, spawning from 

 midsummer to about October. The 

 fall chinooks enter the rivers from 

 midsummer to September, spawn- 

 ing from August to October in 



23 



