HATCHERY OPKRATIONS 67 



regulated by metabolism. If the carrying capacity of a unit is known for a 

 particular size and species of fish at any water temperature, then the carry- 

 ing capacity for another size of the same species held at other water tem- 

 peratures will be the weight of fish that would consume the same amount 

 of feed. 



FLOW INDEX 



The feeding guide developed by Buterbaugh and Willoughby demonstrates 

 a straight line relationship between the length of fish in inches and percent 

 body weight to feed (Figure 26). At a Hatchery Constant of 10, 100 pounds 

 of 2-inch fish will receive the same quantity of food (5 pounds) as 200 

 pounds of 4-inch fish, or 400 pounds of 8-inch fish. (The Hatchery Con- 

 stant is explained on page 245.) 



Haskell states, "if the carrying capacity of a trough or pond is known for 

 any particular size of fish at a particular temperature, then the safe carry- 

 ing capacity for other sizes and temperatures is that quantity of fish which 

 will require the same weight of feed daily." By Haskell's premise, if 100 

 pounds of 2-inch fish is the maximum load that can be held in a rearing 

 tank, then 200 pounds of 4- inch fish, 300 pounds of 6-inch, or 400 pounds 

 of 8-inch fish also would be maximum loads. 



The following formula was derived for a Flow Index, where fish size in 

 inches was used instead of weight of food fed to calculate the safe carrying 

 capacity for various sizes of trout. 



F=W ^[L XI) 



F = Flow Index 



W = Known permissible weight of fish 



L = Length of fish in inches 



/ = Water inflow, gallons per minute 



To determine the Flow Index [F], establish the permissible weight of 

 fish in pounds [W) at a given water inflow (/) for a given size fish [L). 

 The Flow Index [F) reflects the relationship of pounds of fish per gallons 

 per minute water flow to fish size. 



As an example, 900 pounds of 4- inch trout can be safely held in a race- 

 way supplied with 150 gallons per minute water. What is the Flow Index? 



/■ = 900-(4x 150) 



F = 1.5 



How do you establish the initial permissible or maximum weight of fish 

 when calculating the Flow Index? A Flow Index can be estimated by 



