72 



FISH HATCHERY MANAGEMENT 



>- 

 < 

 Q 



X 



to 



C/5 

 OQ 



O 

 O 



4.5 

 4.0 



3.5 



3.0 



2.5 



2.0 

 1.5 



o 



CO 



0.51 



_L 



_L 



4 5 6 



LENGTH IN INCHES 



10 



Figure 27. Oxygen consumption of well-fed and fasted channel 

 catfish at 79°F water temperature. Environmental oxygen levels were 

 6-7 ppm. (Modified from Andrews and Matsuda 1975.) 



per cubic foot of rearing space, have on carrying capacity? Economic con- 

 siderations dictate that the loading density be maintained as high as is 

 practical. However, a reduction in density of fish has been reported by 

 some fish culturists to result in better quality fish, even though there was 

 no apparent environmental stress in their original crowded situation. 



Most carrying capacity tables are based on the maximum fish load possi- 

 ble without excessive dissolved oxygen depletion, and ignore the pathogen 

 load of the water supply. It is known that in steelhead rearing ponds, 

 parasites apparently cannot be controlled by formalin treatments if the 

 loading exceeds seven to eight pounds of fish per gallon of water per 

 minute at 60-70°F. Carrying capacities that include disease considerations 

 and are conducive to optimum health of spring chinook and coho salmon 

 are shown for standard 20 x 80- foot raceways in Table 10. 



This information supports the principle that as fish size increases, fish 

 loading can be increased proportionally. An example of this principle is shown 



