Comparison of the Efficacy of Iodine, Formalin, Salt, and Hydrogen Peroxide for Control of External Bacteria on Rainbow Trout Eggs

Abstract

Two experiments were conducted in vivo with eggs of rainbow trout Oncorhynchus mykiss to compare the bactericidal ability of four common disinfectants. A third test compared bacterial abundance estimation methods for fish eggs (use of a vortex mixer for agitating an egg versus rolling the egg across a petri dish). In the first test, the number of colony forming units (CFU) counted on enriched Ordahl's agar with tobramycin (EOT) or trypticase soy agar (TSA) was compared among eggs treated with various doses of iodine, hydrogen peroxide, formalin, or rock salt. A treatment of 1,667 mg of formalin/L of water and all iodine, salt, and hydrogen peroxide treatments had significantly fewer bacteria on EOT than did controls, but CFU counts for a formalin treatment of 500 or 1,000 mg/L did not. All chemical treatments significantly reduced CFU counts on TSA relative to controls except salt at 0.030 mg/L and formalin at 500 mg/L. The least growth was observed on iodine-treated eggs. In the second experiment, we evaluated the effect of keeping the eggs suspended (i.e., constantly tumbling) during disinfection to increase chemical contact. Treatments were (1) static application of iodine at 100 mg/L, (2) suspension in iodine at 100 mg/L, (3) static application of iodine at 500 mg/L, (4) suspension in iodine at 500 mg/L, (5) suspension in formalin at 2,000 mg/L, (6) suspension in hydrogen peroxide at 2,000 mg/L, (7) static control, and (8) suspended control. Bacterial abundance was significantly reduced in suspended eggs in some cases but not others. Formalin and hydrogen peroxide reduced bacterial abundance but were inferior to iodine in some cases. Each chemical treatment resulted in the survival of bacteria despite attempts to attain better chemical contact by egg suspension. Comparison of the methods used to estimate total CFU per egg indicated that agitation recovered 71-100% of the bacteria on the outside of the egg. Hatchery managers should be aware that not all bacteria are killed by chemical treatment of eggs, and therefore a significant number of pathogens could still enter a hatchery via the importation of treated eggs.

Evaluating the effectiveness of common disinfectants at preventing the propagation of Mycobacterium spp. isolated from zebrafish

“…Iodine is already an established embryo disinfectant in salmonid culture (Wood 1979, Game 1983, Game 1988, Service 2004, Wagner, Arndt et al 2008). We first tested PVPI disinfection on M. chelonae , a frequent zebrafish pathogen, at multiple concentrations (12.5 ppm, 25 ppm, 50 ppm, and 100 ppm) for a 5 minute duration.…”

“…For Mycobacterium spp., however, a higher concentration of hydrogen peroxide seems to be necessary as recommendations for using hydrogen peroxide to disinfect Mycobacterium tuberculosis include the usage of concentrations greater than 30,000 ppm (Noga, 2010). Iodine disinfection of embryos is a widely used and accepted practice in salmonid fisheries with a recommended immersion in 100 ppm povidone-iodine (PVPI) for 10 minutes (Wood, 1979; Alaska Department of Fish and Game, 1983, 1988; United States Fish and Wildlife Service, 2004; Wagner et al, 2008). Immersion in PVPI is also used for generating gnotobiotic zebrafish at 100 pm for 2 minutes (Milligan-Mhyre et al 2011).…”

Advanced treatment of liquid swine manure using physico-chemical treatment

“…Iodine is commonly used in the aquiculture sector [30,31]. As shown in Table 2, the addition of SAP (Phase 1) caused a decrease in the total and fecal coliforms' levels (detection limits of 1 CFU per 100 mL) since the SAP itself yields 20 mg/L of free iodine.…”

Evaluation of oxidative stress markers in the heart and liver of rainbow trout (Oncorhynchus mykiss walbaum) exposed to the formalin

“…Barnes and Soupir (2007) have recommended either daily 15-min formalin treatments at concentrations of at least 750 mg/L or every-other-day treatments at 1667 mg/L to adequately control fungus and maximize rainbow trout egg survival. Wagner et al (2008) have compared the bactericidal ability of four common disinfectants (formalin, iodine, rock salt, and hydrogen peroxide) in vivo on rainbow trout eggs. Formalin and hydrogen peroxide reduced bacterial abundance but were inferior to iodine in some cases.…”