90 FISH HATCHERY MANAGEMENT 



ponds, especially on how well the water is naturally buffered with bicar- 

 bonates. Agricultural extension agents and the Soil Conservation Service 

 can provide detailed advice about water chemistry and lime applications. 



Normally, a limed pond will be safe for stocking within 10 days after 

 treatment, or when the pH has declined to 9.5. However, a normal food 

 supply will not be present until three to four weeks later. 



Chlorine has been used by fish culturists as a disinfecting agent. Ten 

 parts per million chlorine applied for 24 hours is sufficient to kill all harm- 

 ful bacteria and other organisms. Several forms of chlorine can be obtained. 

 Calcium hypochlorite is the most convenient to apply. It contains 70% 

 chlorine and is readily available. It can be applied to either flooded or 

 dewatered ponds. 



A 600 parts per million solution of Hyamine 1622, Roccal, or Hyamine 

 3500 may be used for disinfecting ponds. Twice this strength may be used 

 to disinfect equipment and tools. The strength of the disinfecting solution 

 is based on the active ingredient as purchased. 



Water Supply Structures 



The water supply for a fish hatchery should be relatively silt-free and de- 

 void of vegetation that may clog intake structures. For this reason, an 

 earthen ditch is not recommended for conveying water because of algal 

 growth and the possibility of aquatic vegetation becoming established. At 

 hatcheries with a silt problem, a filter or settling basin may be necessary. 

 The water intake structure on a stream should include a barred grill to ex- 

 clude logs and large debris and a revolving screen to remove smaller debris 

 and stop fish from entering the hatchery. 



There are a vast number of methods used to adjust and regulate water 

 flows through fish rearing units. Some of these include damboards, head- 

 boxes with adjustable overflows, headgates, headboards with holes bored 

 through them, molasses valves, faucet- type valves, and flow regulators. 

 Each type has advantages. 



Generally, damboards and headboxes will not clog, and they provide a 

 safe means of regulating water flows. They are particularly useful with 

 gravity water supplies, but they are not easily adjusted to specific water 

 flows. Valves and flow regulators are readily adjustable to specific water 

 flows and are preferred with pressurized water supplies, but are prone to 

 clogging if any solid material such as algae or leaves is present in the 

 water. 



Water flows can be measured with a pail or tub of known volume and a 

 stop watch when valves or gates are used to regulate the water flow. Dam 

 boards can be modified to serve as a rectangular weir for measuring flows 

 (Appendix D). 



