Efficacy of formalin and hydrogen peroxide to increase survival of channel catfish infected with saprolegniasis

The efficacy of formalin and hydrogen peroxide to increase survival associated with external saprolegniasis on fingerlings of channel catfish Ictalurus punctatus was evaluated in four laboratory trials. Fungal epizootics were initiated according to procedures developed in a fungal-disease model. Fish were abraded with a dremel tool and then placed in an aerated static infection tank containing fungal-infected hemp seeds held in teaballs that were suspended in 100 L of water for 24 h (trials 1–3) or 6 h (trial 4). In the formalin trials, treatment regimens of 0, 82, and 166 mg/L (trial 1) or 0 and 83 mg/L (trial 2) were administered to channel catfish for 60 min once every other day for a total of three treatments (trial 1) or once daily for a total of seven treatments (trial 2). In the hydrogen peroxide trials, treatment regimens of 0, 75, and 102 mg/L (trial 3) or 0 and 75 mg/L (trial 4) were administered to channel catfish for 60 min once every other day for a total of three treatments. Each treatment regimen was tested in triplicate, with 10 fish per replicate. Formalin exposures of 83 (seven treatments; 33% survival) and 166 mg/L (three treatments; 63% survival) for 60 min significantly (P ≤ 0.01) increased channel catfish survival in comparison with controls (of which 3% and 13%, respectively, survived). In trial 4, hydrogen peroxide exposure of 75 mg/L (63% survival) for 60 min significantly (P ≤ 0.01) increased channel catfish survival in comparison with the untreated controls (13% survival). Formalin and hydrogen peroxide treatments were effective in increasing survival in channel catfish infected with fungus.