BROODSTOCK, SPAWNING, AND EGG HANDLING 195 



are placed in slots in the trough to force the waterflow up through each 

 stack. 



Many eggs can be handled in this type of unit, but it is difficult to ob- 

 serve egg development during incubation, and all trays in a stack must be 

 removed in order to examine the eggs on any individual tray. Possible air 

 locks within the stack can cause poor water circulation through the eggs. 



CATFISH TROUGHS 



Channel catfish eggs, which are deposited in a cohesive mass, require spe- 

 cial devices when they are moved to a hatching trough for artificial incuba- 

 tion. The large egg masses usually are broken up into smaller pieces to 

 enhance aeration and then placed in suspended baskets similar to the trays 

 described in the previous section. 



When catfish eggs are hatched in troughs, they must be agitated by pad- 

 dles supported over the trough and driven by an electric motor or a water 

 wheel (Figure 67). The agitation must be sufficient to gently move the 

 whole egg mass. Paddles are constructed of galvanized tin or aluminum 

 and attached to a rotating shaft. The paddles are commonly 4 inches wide 

 and long enough to dip well below the bottom of the baskets as they turn. 

 The pitch of the paddles is adjusted as required to insure movement of 

 spawns in the baskets. The preferred speed is about 30 revolutions per 

 minute. 



HATCHING BASKETS 



Hatching baskets are quite similar to hatching trays, except that they are 

 approximately 6 to 12 inches deep and suspended in the trough to permit 

 a horizontal water flow. In many cases, deflector plates are installed ahead 

 of each basket in such a way as to force the flowing water up through the 

 baskets for better circulation. In the case of Pacific salmon, as many as 

 ,50,000 eggs may be placed in a single basket. 



HATCHING JARS 



Hatching jars usually are placed in rows on racks with a manifold water 

 supply trough providing inlets to each jar and a waste trough to catch 

 overflow water (Figure 68). A simple unit can be fabricated from 2-inch 

 supply pipe with taps and an ordinary roof gutter as the waste trough. An 

 open tee usually is installed between the supply line and the pipe to the 

 bottom of the jar to aid in the elimination of gas bubbles during incuba- 

 tion of salmonid eggs, which must not be distrubed. The open tee may also 

 be used to introduce chemicals for treating eggs. The diameter of the tee 



