Investigations in Fish Control: 99. Evaluation of 215 Candidate Fungicides for Use in Fish Culture

The fungicidal activity of 215 compounds was evaluated by comparing their effectiveness with that of malachite green. More than half were found to be unsuitable as aquatic fungicides in preliminary screening tests because of their lack of activity against fungi, toxicity to fish or eggs, insolubility in water, or potential carcinogenicity. After further testing, 30 compounds were selected for evaluation of their activity against fungi on eggs of rainbow trout (Oncorphynchus mykiss). Four compounds-8-quinolinol, 8-quinolinol sulfate, dichlorophen, and formalin-inhibited fungal growths on dead and live fish eggs and demonstrated the greatest potential as replacements for malachite green. The quinolinols cannot be considered for use as aquatic antifungal agents, however, because they were toxic to eggs at efficacious concentrations (=>1.0 mg/L). Dichlorophen, at concentrations of 5.0 mg/L, was effective for eggs of channel catfish (Ictalurus punctatus) that had been separated, but was toxic for eggs clustered in the original egg mass; it showed potential for use on channel catfish eggs at 2.5 mg/L for 15 min, but was only marginally effective against fungi on rainbow trout eggs. Formalin controlled fungal infections on rainbow trout eggs at a concentration of 250 mg/L for 60 min-a concentration substantially lower than has been previously reported.