The quality of eggs tested could also have affected infection rates. The condition of
eggs in this study was excellent as evidenced by the high percent fertility (mean 92%)
and low initial percent mortality. The combination of these factors may have been
responsible for the fact that no statistical difference was observed between the negative
control groups and the prophylactic treatment groups for all chemical efficacy tests.
Hatcheries routinely administer formalin for the control of fungal infections on eggs
at concentrations of 1667-2000 ~1 1-l for 15 min exposures (Piper et al., 1982).
Marking et al. (1994) reported that lower formalin concentrations (250, 500, and 1000
~1 1-l) controlled fungus on cultured rainbow trout eggs at exposures of 60 min. This
study demonstrated that when there is an incidence of fungus on the eggs, formalin
treatments of 1000 or 1500 ~1 I-’ for 15 min are required to control spread of fungus
and to achieve a successful hatch. Lower formalin treatment concentrations are effective
for prophylactic control of fungus (Marking et al., 1994). The use of lower treatment
concentrations could reduce operational costs and decrease levels of formalin discharged
into the environment.