Fish Hatchery Management - fisheries & aquaculture

BROODSTOCK, SPAWNING, AND EGG HANDLINGt97manifold of pipes beneath a perforated aluminum plate in the bottom ofthe box. A screened lip on the upper edge of the box provides an overflowand retains the eggs or fry. The box commonly is used in bulk handling ofeggs to the eyed stage for shipping, but it can also be used to rear fry tothe feeding stage (Figure 69).A problem with the hatching box is the tendency for gas bubbles tobuild up below the perforated plate, shutting off the water flow to portionsof the box. As with other systems, it is good practice to aerate any watersupply used for this type of incubation.VERTICAL-TRAY INCUBATORSThe vertical-tray incubator is widely used for developing salmonid eggs(Figure 70). The eggs are allowed to hatch in the trays and fry remainthere until ready to feed. Water is introduced at one end of the rop trayand flows under the egg basket and up through the screen bottom, circulatingthrough the eggs. Water, upwelling through the bottom screen helpsprevent smothering of hatched fry. The water then spills over into the traybelow. and is aerated as it falls.*rS$. ;FIGURE 68. Jar incubation of muskellunge eggs. (Courtesy Wisconsin Departmentof NaturalResources.)