Jeff J. Rach

Efficacy of formalin, hydrogen peroxide, and sodium chloride on fungal-infected rainbow trout eggs

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 −1 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 parasitica ) rainbow trout eggs ( Oncorhynchus mykiss ) for 15 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 μl l −1 and hydrogen peroxide treatments of 500 and 1000 μl l −1 were the most effective. Sodium chloride treatments of 30 000 mg l −1 improved fry hatch, but the compound was less effective at inhibiting fungal growths compared with hydrogen peroxide and formalin treatments.

Effect of Species, Life Stage, and Water Temperature on the Toxicity of Hydrogen Peroxide to Fish

Abstract Hydrogen peroxide is a drug of low regulatory priority status that is effective in treating fish and fish eggs infected by fungi. However, only limited information is available to guide fish culturists in administering hydrogen peroxide to diseased fish. Laboratory tests were conducted to determine (1) the sensitivity of brown trout Salmo trutta, lake trout Salvelinus namaycush, fathead minnow Pimephales promelas, walleye Stizostedion vitreum, channel catfish Ictalurus punctatus, and bluegill Lepomis machrochirus to hydrogen peroxide treatments; (2) the sensitivity of various life stages of rainbow trout Oncorhynchus mykiss to hydrogen peroxide treatments; and (3) the effect of water temperature on the acute toxicity of hydrogen peroxide to three fish species. Fish were exposed to hydrogen peroxide concentrations ranging from 100 to 5,000 μL/L (ppm) for 15-min or 45-min treatments every other day for four consecutive treatments to determine the sensitivity of various species and life stages of fi...

Safety of formalin treatments on warm- and coolwater fish eggs

Abstract Formalin is widely used for treating fungal infections of fish eggs in intensive aquaculture operations. The use of formalin in the United States is only allowed on salmonid and esocid eggs unless a special exemption is granted for use on other species. This study was conducted to determine the safety of formalin treatments on eggs of representative warm- and coolwater fish species and data was used to support a request to allow the use of formalin on the eggs of warmwater and additional coolwater fish species. Non-eyed eggs of walleye ( Stizostedion vitreum ), common carp ( Cyprinus carpio ), white sucker ( Catostomus commersoni ), channel catfish ( Ictalurus punctatus ), and lake sturgeon ( Acipenser fulvescens ) were cultured in miniature egg hatching jars and treated for 45 min every-other-day with 1500, 4500, or 7500 μL L −1 formalin up to hatch. For all species tested, the percent hatch was greater in 1500 μL L −1 treatment groups than in untreated controls. Walleye eggs were the least sensitive species and had a hatch of 87% in the 7500 μL L −1 treatment. Lake sturgeon were the most sensitive species with a mean hatch of 54% in 1500 μL L −1 treatments. Adequate margins of safety exist for standard treatments (1500 μL L −1 for 15 min) on eggs of all species tested except lake sturgeon. Fungal infections drastically reduced or eliminated hatch in most control groups whereas most treated groups were free of infections. This confirms the efficacy of formalin as an fungicide.

Importance of Analytically Verifying Chemical Treatments

Abstract Hydrogen peroxide is considered a low regμLatory priority compound by the U.S. Food and Drug Administration. It is used to control fungal infections on fish eggs. We studied the treatment profiles of hydrogen peroxide in Heath, McDonald egg jar, and Clark–Williamson incubators during treatments intended to deliver an effective regimen of at least 500 μL hydrogen peroxide/L (i.e., treatments of 500 and 1,000 μL/L) for 15 min. Hydrogen peroxide concentrations decreased with increasing distance from the influent water in both Heath and Clark–Williamson incubators. The top treatment tray (tray 2) of the Heath incubator received more than 90% of the intended regimen during the 500 μL/L treatment, whereas at 1,000 μL/L, all trays had hydrogen peroxide concentrations at or above 500 μL/L for 15 min. None of the compartments in the Clark–Williamson incubator received the intended therapeutic regimen when treated at 500 μL/L. The McDonald egg jar system distributed the intended concentration for the desig...

Toxicity of Hydrogen Peroxide Treatments to Rainbow Trout Eggs

Abstract Hydrogen peroxide treatments of 0, 500, 1,000, and 3,000 μL/L, concentrations that were multiples of the Low Regulatory Priority limit of 500 μL/L, were administered for 15 min every weekday (Monday–Friday) to eggs of rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) to determine the margin of safety existing for standard egg treatments. All untreated and treated eggs remained free of fungal infection throughout incubation. Hydrogen peroxide treatment reduced the mean percent hatch of rainbow trout eggs by 1.4–5.9% among those treated at 500 μL/L, 6.8–15.4% among those treated at 1,000 μL/L, and 13.2–25.3% among those treated at 3,000 μL/L. Mean percent hatch of rainbow trout eggs treated at 1,000 μL H2O2/L was 7% lower than that for eggs treated at 500 μL H2O2/L. Mean percent hatch of Skamania strain steelhead was significantly reduced by hydrogen peroxide treatment, whereas the mean percent hatch of Ganaraska strain steelhead was similar to the mean percent hatch of rai...

Efficacy of Hydrogen Peroxide versus Formalin Treatments to Control Mortality Associated with Saprolegniasis on Lake Trout Eggs

Abstract We compared the efficacy of hydrogen peroxide versus formalin treatments to control fungal infections on eggs of lake trout Salvelinus namaycush incubated at a hatchery in Wisconsin. Four strains of lake trout eggs were incubated in six vertical-flow Heath incubators; three replicate incubators for each chemical. Each incubator had 13 trays containing approximately 25,000–30,000 eggs/tray. Formalin (1,667 mg/L) or hydrogen peroxide (1,000 mg/L) treatments were administered once daily for 15 min up to the development of visible eye spots in the eggs (eyed egg stage). Eyed and dead eggs were separated using a photoelectric egg sorter, and the number of live and dead eggs was determined volumetrically. In the hydrogen peroxide test group, the bottom trays of each incubator had fungus present on the eggs, whereas no fungus was observed on eggs treated with formalin. The mean percentage of eyed eggs for an incubator treated with formalin (75%) was significantly greater than an incubator treated with h...

Toxicity of Rotenone and Antimycin to Silver Carp and Bighead Carp

Abstract The general public, natural resource managers, and government agencies have become increasingly concerned about the continued spread of silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis in the Mississippi River basin and their potential spread into the Great Lakes. An integrated approach of chemical, biological, and physical measures is needed to reduce Asian carp populations in these waters. Rotenone and antimycin are the only general piscicides that are registered with the U.S. Environmental Protection Agency for controlling fish populations. Considerable information is available regarding the toxicity of these chemicals to numerous fish species. However, there is little available toxicity information indicating the potential for these chemicals to control Asian carp. In this study, Prenfish (5% rotenone) and antimycin (90% antimycin-A) toxicities to silver carp and bighead carp were assessed in acute toxicity and effective contact time tests. Each acute toxicity test consiste...

Effects of Water Hardness on Size and Hatching Success of Silver Carp Eggs

Abstract Eggs of silver carp Hypophthalmichthys molitrix absorb water after release from the female, causing them to become turgid and to increase substantially in size. The volume of water that diffuses within an egg is most likely determined by (1) the difference in ionic concentration between the egg and the water that surrounds it and (2) the elasticity of the egg membrane. Prior observations suggest that silver carp eggs may swell and burst in soft waters. If water hardness affects silver carp reproductive success in nonnative ecosystems, this abiotic factor could limit silver carp distribution or abundance. In this study, we tested the effect of water hardness on silver carp egg enlargement and hatching success. Groups of newly fertilized silver carp eggs were placed in water at one of five nominal water hardness levels (50, 100, 150, 200, or 250 mg/L as CaCO3) for 1 h to harden (absorb water after fertilization). Egg groups were then placed in separate incubation vessels housed in two recirculation...

Method for Inducing Saprolegniasis in Channel Catfish

Abstract A method was developed to uniformly and systematically induce saprolegniasis in channel catfish Ictalurus punctatus. Three different methods for inducing saprolegniasis were evaluated in waters containing known zoospore concentrations of Saprolegnia parasitica: (1) low-temperature shock to induce immunosuppression; (2) physical abrasion stress; and (3) a combination of both low temperature shock and abrasion stress. Low-temperature shock or abrasion stress alone were not effective for inducing saprolegniasis. Only 10% of fish stressed by low-temperature shock alone became infected. No fish receiving abrasion stress treatments alone became infected even though these fish were subject to significant abrasion and dewatering stress. A combination of low-temperature and abrasion stress, however, was sufficient to induce saprolegniasis in 100% of fish tested and resulted in 90% mortality. No fish became infected in the positive control group (exposed to zoospores of S. parasitica without stress) or in ...

Analytical Verification of Waterborne Chemical Treatment Regimensin Hatchery Raceways

Abstract Chemical therapy for control and prevention of fish diseases is a necessary and common practice in aquaculture. Many factors affect the accuracy of a chemical treatment application, such as the functioning of the chemical delivery system, calculation of chemical quantities to be delivered, water temperature, geometry of the culture unit, inlet-outlet structure, the influence of aerators, wind movement, and measurement of water volumes and flow rates. Three separate trials were conducted at the Osceola Fish Hatchery, a facility of the Wisconsin Department of Natural Resources, evaluating the accuracy of flow-through hydrogen peroxide treatments applied to 1, 3, or 9 raceways that were connected in series. Raceways were treated with 50 or 75 μL/L of hydrogen peroxide for 30 min. Chemical concentrations were determined titrimetrically. The target treatment regimen was not realized in any of the applications. Chemical concentrations dropped and exposure times increased with each additional raceway tr...