peratiire of the cool room may be 

 maintained by the effect of the ad- 

 joining cold room, but more often 

 a separate refrigeration unit is 

 necessary to maintain the cool- 

 room temperature just above freez- 

 ing. 



Animal and fish meals often are 

 used in fish hatcheries. These 

 products are stored in rodentproof 

 rooms or bins, usually in the loft 

 over the food-preparation room. 

 Downspouts from the bins, with 

 controls, make the meals easily 

 available in the feed room. (See 

 fig. 22.) 



Rearing Ponds 



Eearing ponds specifically de- 

 signed for the most convenient and 

 efficient operation are required at 

 salmon hatcheries. These ponds 

 are of a variety of sizes and shapes, 

 but certain designs have proved 

 most successful. 



The early ponds used for rearing 

 of young salmon, particularly chi- 

 nook and silver, were earthen, usu- 

 ally very long and narrow, and had 

 the water flowing from one pond 

 through a second and often through 

 several j^onds. The ponds at the 

 modern salmon hatcheries are of 

 concrete, and the tendency is to pro- 

 vide a good flow of water and use 

 it only once when an adequate water 

 supply is available. This practice 

 permits easier cleaning of the ponds. 

 In certain types of ponds the flow of 

 water over the concrete bottom, as 

 well as the movements of the fish, 

 tends to concentrate debris at the 

 outlet of the pond. Probably the 

 greatest advantage of the concrete 

 pond is in this cleanliness, there 



being minimum lodgement of dis- 

 ease organisms; whereas the oppo- 

 site is true of the earthen ponds. 

 When disease must be treated with 

 chemicals, the concrete pond lends 

 itself to such treatment. In gen- 

 eral, despite the greater construc- 

 tion cost, the concrete pond is pref- 

 erable to earthen ponds. 



Probably the most common type 

 of rearing pond at salmon hatch- 

 eries is the raceway, in which a sub- 

 stantial and uniformly dispersed 

 flow is maintained from the water- 

 intake end to the lower or screened 

 end. (See fig. 19.) Ponds of this 

 type are preferred at Fish and 

 Wildlife Service hatcheries. The 

 ponds are usually 8 feet wide and 

 80 feet long and have an average 

 water depth of 2.5 feet. From the 

 upper to the lower end, the bottom 

 has a slope of 1 inch in each 10 feet 

 of length. The inflow of water is 

 200 to 400 g. p. m., and spills from 

 a head trough into the pond in a 

 slieet as wide as the pond. This 

 manner of introducing water pro- 

 vides as nearly as possible a uni- 

 form movement of water down the 

 pond witliout dead-water areas. 

 The screen and dam boards also ex- 

 tend the full width of the pond. 

 Tlie removable screen (of appro- 

 priate mesh, galvanized after weav- 

 ing) or a perforated plate, placed 

 in slots or grooves in the concrete 

 at the lower end of the pond, pre- 

 vents the escape of fish. The dam 

 boards, also removable, are located 

 downstream IVoiu the screen and 

 maintain the (U'sired ])()nd level. At 

 some liatchei-ies (he lowei' end of the 

 l)()ii(l is seak'd by a concrete Avail 

 and the overflow i>oes down a stand- 



46 



