hatchery operations 71 



Table 9. dissolved oxygen in parts per million for fresh water in equili- 

 brium WITH air. (SOURCE: LEITRITZ AND LEWIS 1976.) 



reduced. In this way, maximum rearing unit and water flow requirements 

 will be delineated and frequent adjusting of water flows or fish transfers 

 can be avoided. 



Generally, these methods are limited to intensive culture of fish in situa- 

 tions where oxygen availability is regulated by the inflowing water. In ex- 

 tensive culture systems involving large ponds, oxygen availability depends 

 to a greater extent on oxygen replacement through the surface area of the 

 water. Water inflow in such situations is not as significant as pond surface 

 area and water volume in determining carrying capacity. 



Estimates of oxygen consumption under intensive cultural conditions 

 have been determined for channel catfish. Oxygen consumption rates de- 

 cline as the available oxygen decreases, and there is a straight- line (semi- 

 log) relationship between fish size and oxygen consumption; smaller fish 

 require more oxygen per unit size than larger fish (Figure 27). 



The data in Figure 27 can be used to estimate the carrying capacity for 

 channel catfish if the available oxygen in a rearing unit is determined. Ox- 

 ygen consumption will change proportionately as the water temperature in- 

 creases or decreases. 



DENSITY INDEX 



Carrying capacity has been discussed in relation to water inflow or, more 

 specifically, oxygen availability. What affect does density, as pounds of fish 



