adults as a result of injury and 

 disease. At the Grand Coulee sta- 

 tions of the Fish and Wildlife Serv- 

 ice, nmch attention has been given 

 to the development of satisfactory 

 ponds. The most successful pond 

 yet devised, and one in which spring 

 chinooks have been held very satis- 

 factorily, is described by Koger 

 Burrows (unpublished) of the Fish 

 and Wildlife Service. 



The retention of the fish until sexual 

 maturity must meet two main require- 

 ments for successful operations. First, 

 it must prevent mechanical injury to the 

 adult stock, and second, it must inhibit 

 the development of disease. 



(1) It is characteristic of adult salmon 

 when barred from further upstream prog- 

 ress to circle the area of impoundment, 

 attempt to move upstream, and finally 

 return to the upstream barrier and at- 

 tempt to surmount it by jumping. Fish 

 thus trapped will circle and mill around 

 restlessly for 10 days to 2 weeks but 

 eventually will settle down in the deeper 

 portions of the area to await maturity. 

 By that time, however, the damage has 

 been done as far as mechanical injury 

 is concerned. Fish have jumped out on 

 the banks and died or returned to the 

 pond severely abraded, injured them- 

 selves by hitting obstructions, or worn 

 their nose fighting the upstream barrier. 

 Any traumatic condition resulting from 

 mechanical injury no matter how minute 

 opens an avenue for infection and the 

 death of the fish may result. 



It is a relatively simple matter to pre- 

 vent fish from jumping in a retaining 

 area. Fish jump at the point of water 

 inflow but they also jump at vertical 

 banks. To prevent the latter all banks 

 in an artificial pond should have at least 

 a 45° slope. Salmon before making a 

 jump nose along at the surface of the 

 water. If the water surface is covered 

 the fish will not jump. Taking advan- 

 tage of this characteristic the water sur- 

 face in the area immediately below the 

 obstruction is completely covered by 

 floating strips of canvas. 



By the use of a submerged culvert the 

 water may be introduced into the cen- 

 ter of the upper section of the pond so 

 that the fish can jump but still do them- 

 selves no harm by striking the banks. 

 As far as is know^n jumping by salmon 

 produces no ill effects as long as mechan- 

 ical injury is not incurred. This type 

 of barrier to the upstream migration has 

 two advantages over the usual weir, first, 

 the fish do not fight the upwelling water 

 sufficiently to cause abrasions and, sec- 

 ond, if properly placed or covered, jump- 

 ing will either do no harm or can be 

 prevented. 



(2) The type of holding area and the 

 water temperature are the two major 

 factors concerned with the development 

 or inhibition of disease. 



A holding area to be satisfactory must 

 have a continuing and fairly rapid inter- 

 change of water throughout the entire 

 impoundment. Natural pools fulfill this 

 requirement otherwise they would silt 

 up and no longer be pools. Salmon pre- 

 fer deep water in which to lie between 

 migrations but this preference should not 

 be satisfied at the sacrifice of water 

 interchange. If relatively stagnant 

 water is present in the deeper portions 

 of the area, disease organisms which are 

 waterborne have an opportunity to con- 

 centrate in these portions. As these 

 areas are the parts preferred by the fish 

 the infections become dominant and the 

 natural resistance of the fish is not sufii- 

 cient to cope with the disease. A good 

 holding area, therefore, should have a 

 bottom contour such as to avoid the 

 development of areas of semistagnant 

 water. 



The temperature of the water is, also, 

 an important factor which controls the 

 development of disease. Both fungus 

 {Saprolegnia imrusitica) and columnaris 

 {Chondrococcus columnaris), the princi- 

 pal causes of mortality in adult fish, do 

 not reach their point of optimum develop- 

 ment at temperatures below 60° F. For 

 this reason holding areas in which the 

 water temperature does not rise above 

 60° may be operated with a smaller water 

 inflow and, consequently, a slower rate 

 of interchange than areas which have 



