EFFECT OF WATER-FLOW RATES IN HATCHING JARS TO CONTROL FUNGAL-INFECTIONS OF RAINBOW-TROUT EGGS

The successful culture of fish eggs often depends on chemical treatmen t to control fungus. Attempts to control fungus without chemicals have centered on the use of elevated water flow to roll fish eggs in hatch ing jars. We cultured uninfected and fungus-infected eggs of rainbow t rout (Oncorhynchus mykiss) at various flow rates. Eggs that were cultu red at 300- and 600-mL/min flow rates exhibited no egg movement, highe r rates of fungal infection, and reduced hatching success. Eggs cultur ed at a 1,200-mL/min flow were lifted into the water column and rolled moderately; this flow rate significantly increased the percent hatch due to control of fungus. A flow of 1,800 mL/min vigorously rolled the eggs and controlled fungus, but it also resulted in increased egg mor tality. The use of water flow to roll eggs controlled fungal infection s and may reduce, or in some circumstances eliminate the need for chem ical treatment. The success of this physical method of treatment is de pendent on hatchery personnel maintaining flow rates at levels that in duce a moderate rolling of the eggs, which inhibits fungal infections without damaging eggs.