Abstract
Antifungal agents are essential for the maintenance of healthy stocks of fish and their eggs in
intensive aquaculture operations. In the USA, formalin is the only fungicide approved for use in
fish culture. However, hydrogen peroxide and sodium chloride have been granted low regulatory
priority drug status by the United States Food and Drug Administration (FDA) and their use is
allowed. We evaluated the efficacy of these fungicides for controlling fungal infections on
rainbow trout eggs. A pilot study was conducted to determine the minimum water flow rate
required to administer test chemicals accurately in Heath incubators. A minimum water flow rate
of 7.6 1 min-’ was necessary to maintain treatment concentrations during flow-through chemical
exposures. The antifungal activity of formalin, hydrogen peroxide, and sodium chloride was
evaluated by treating uninfected and 10% fungal-infected (Saprolegnia parasirica) rainbow trout
eggs (Oncorhynchus mykiss) for 1.5 min every other day until hatch. There were no significant
differences among treatments in percent hatch or final infection for uninfected eggs receiving
prophylactic chemical treatments. Eggs of the negative control group (uninfected and untreated)
had a mean hatch exceeding 86%. All chemical treatments conducted on the infected egg groups
controlled the spread of fungus and improved hatching success compared with the positive control
groups (infected and untreated). Formalin treatments of 1000 and 1500 I_LI I- ’ and hydrogen
peroxide treatments of 500 and 1000 ~1 1-l were the most effective. Sodium chloride treatments
of 30000 mg I-’ improved fry hatch, but the compound was less effective at inhibiting fungal
growths compared with hydrogen peroxide and formalin treatments.
Keywords: Antifungal; Hydrogen peroxide; Formalin; Sodium chloride