|Straus, David - Dave|
Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2009
Publication Date: 3/15/2009
Citation: Mitchell, A.J., Radomski, A.A., Straus, D.L., Carter, R.R. 2009. The effect of hydrogen peroxide on the hatch rate and Saprolegnia spp. infestation of channel catfish eggs. North American Journal of Aquaculture. 71:276-280. Interpretive Summary: Aquatic fungi infest channel catfish spawns (eggs held together in gelatinous masses) in commercial hatching containers and can lower the number of surviving fry (small fish that hatch from eggs). Previous studies showed that hydrogen peroxide limits fungal infections on various fish eggs and can increase fry survival, however no studies have documented the effect of hydrogen peroxide on channel catfish eggs infested with identified fungal organisms. Daily hydrogen peroxide treatments at the rates of 0, 15.6, 31.3, 62.5, 125, 250, 500, 1,000, 2,000, and 4,000 mg/L were applied in an experimental hatching trough system while water (24°C) was flowing at a rate of one water exchange in 30 min. The egg to water density was 2.5 g/L. All hydrogen peroxide concentrations significantly reduced fungal growth when compared to the controls and those concentrations more than 500 mg/L drastically lowered fry survival. The 250 mg/L treatment had the highest survival (64.4% compared to 24.7% for the controls), lowest fungal incidence (27.3% compared to 100%) and the lowest fungal coverage (0.95 cm compared to 7.23 cm). The fungi infesting the eggs in our studies were identified, using a genetic method (PCR), as members of the genus Saprolegnia, a common group of fungi known to infest fish and fish eggs.
Technical Abstract: Infestations of fungi or water molds on channel catfish Ictalurus punctatus eggs can lower egg survival requiring the producer to spawn more catfish or risk fingerling shortages. Hydrogen peroxide treatments were evaluated to determine their effect on egg survival and efficacy against naturally occurring fungi infestations in a channel catfish hatching system that simulates the trough hatching system used in most commercial hatcheries. Treatments were applied while water was flowing at a rate of one water exchange/30 min and egg density used in our studies was 2.5 g/L. Experiments were run at water temperatures of 23.2–24.0°C, dissolved oxygen concentrations of 4.5–6.8 mg/L (53–79% saturation), total alkalinity of 209–217 mg/L and total hardness of 91–110 mg/L. Observations for fungal development were made daily and the maximum measure of fungal growth was recorded; fungi infecting channel catfish eggs were identified as Saprolegnia spp. At the termination of each experiment, a determination of the fry survival percentage (number of eggs/number of fry X 100) was made. An initial range finding study, hydrogen peroxide applied once daily for 5 d as a flow-through treatment at six concentrations (0, 250, 500, 1,000, 2,000, and 4,000 mg/L) until the eggs were in the eyed-egg stage, demonstrated that concentrations above 500 mg/L lowered egg survival. In two subsequent experiments, identical treatments (0, 15.6, 31.3, 62.5, 125, 250, 500 mg/L) were applied for 6 d in each study. Concentrations of 125, 250 and 500 mg/L were significantly different from the controls and all treatments significantly reduced fungal coverage when compared to the controls but were not different from each other. The 250 mg/L treatment had the highest mean survival (64.4% compared to 24.7% for the controls), lowest incidence of fungi (27.3% compared to 100% for the control) and the lowest average fungal coverage (0.95 cm compared to 7.23 cm for the controls).