196 FISH HATCHERY MANAGEMENT 



Figure 67. Channel catfish trough for egg incubation. Paddles (arrow) gently 

 circulate the water in the trough. (FWS photo.) 



should be larger than the pipe entering the jar to prevent venturi action 

 from sucking air bubbles into the jar. 



Hatching jars are designed to provide an upward flow of water intro- 

 duced at the bottom of the jar. When rolling of the eggs is desired, as in 

 the case of some coolwater species, the bottom of the jar is concave, with 

 the water introduced at the center. When used for incubating trout or sal- 

 mon eggs, the jar is modified with a screen-supported gravel bottom, and 

 the water is introduced underneath the gravel. This provides a uniform, 

 upward water flow, and the eggs are stationary. These systems also have 

 been used for striped bass and channel catfish egg incubation. 



Some fry will swim out of the jar and into the waste trough if a cover 

 screen is not provided. Coolwater species are allowed to swim from the jars 

 and are collected in holding tanks. 



MONTAN./>k HATCHING BOX 



The Montana Hatching Box operates essentially like a hatching jar. The 

 box is constructed of waterproof plywood or fiberglass and is approxi- 

 mately 1 foot square by 2 feet high. A vertical water flow is provided by a 



