BROODSTOCK, SPAWNING, AND EGG HANDLING 



197 



manifold of pipes beneath a perforated aluminum plate in the bottom of 

 the box. A screened lip on the upper edge of the box provides an overflow 

 and retains the eggs or fry. The box commonly is used in bulk handling of 

 eggs to the eyed stage for shipping, but it can also be used to rear fry to 

 the feeding stage (Figure 69). 



A problem with the hatching box is the tendency for gas bubbles to 

 build up below the perforated plate, shutting off the water flow to portions 

 of the box. As with other systems, it is good practice to aerate any water 

 supply used for this type of incubation. 



VERTICAL-TRAY INCUBATORS 



The vertical- tray incubator is widely used for developing salmonid eggs 

 (Figure 70). The eggs are allowed to hatch in the trays and fry remain 

 there until ready to feed. Water is introduced at one end of the top tray 

 and flows under the egg basket and up through the screen bottom, circulat- 

 ing through the eggs. Water, upwelling through the bottom screen helps 

 prevent smothering of hatched fry. The water then spills over into the tray 

 below, and is aerated as it falls. 



Figure 68. Jar incubation of muskellunge eggs. (Courtesy Wisconsin Depart- 

 ment of Natural Resources.) 



