Jj. Rach et al., EFFECT OF WATER-FLOW RATES IN HATCHING JARS TO CONTROL FUNGAL-INFECTIONS OF RAINBOW-TROUT EGGS, The Progressive fish-culturist, 57(3), 1995, pp. 226-230
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.