Fish Hatchery Management - fisheries & aquaculture

BROODSI'OCK, SPAWNING, AND ECG HANDLING 195are placed in slots in the trough to force the waterflow up through eachstack.Many eggs can be handled in this type of unit, but it is difficult to observeegg development during incubation, and all trays in a stack must beremoved in order to examine the eggs on any individual tray. Possible airlocks within the stack can cause poor water circulation through the eggs.CA'fFISH TROUGHSChannel catfish eggs, which are deposited in a cohesive mass, require specialdevices when they are moved to a hatching trough for artificial incubation.The large egg masses usually are broken up into smaller pieces toenhance aeration and then placed in suspended baskets similar to the traysdescribed in the previous section.When catfish eggs are hatched in troughs, they must be agitated by paddlessupported over the trough and driven by an electric motor or a waterwheel (Figure 67). The agitation must be sufficient to gently move thewhole egg mass. Paddles are constructed of galvanized tin or aluminumand attached to a rotating shaft. The paddles are commonly 4 inches wideand 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 ofspawns in the baskets. The preferred speed is about l']0 revolutions perminute.HA'I'CHING BASKFJ,TSHatching baskets are quite similar to hatching trays, except that they areapproximately 6 to l2 inches deep and suspended in the trough to permita horizontal water flow. In many cases, deflector plates are installed aheadof each basket in such a way as to force the flowing water up through thebaskets for better circulation. In the case of Pacific salmon, as rnany as50,000 eggs may be placed in a single basket.I"IATCHING JARSHatching jars usually are placed in rows on racks with a manifold watersupply trough providing inlets to each jar and a waste trough to catchoverflow water (Figure 68). A simple unit can be fabricated from 2-inchsupply pipe with taps and an ordinary roof gutter as the waste trough. Anopen tee usually is installed between the supply line and the pipe to thebottom of the jar to aid in the elimination of gas bubbles during incubationof salmonid eggs, which must not be distrubed. The open tee may alsobe used to introduce chemicals for treating eggs. The diameter of the tee