Pseudoloma neurophilia, a microsporidium that primarily infects neural tissues, is a common pathogen in laboratory zebrafish. The risk of parasite transmission with different spawning apparatuses and the effectiveness of disinfection are unknown. In this study, we spawned uninfected zebrafish with P. neurophilia-infected zebrafish in either 50 L mass spawning chambers (MSCs) or 1 L standard breeding tanks (BTs). Fish were spawned once or thrice, with and without chamber disinfection between uses, to evaluate risk of vertical and horizontal transmission. Six disinfection protocols were tested to determine which effectively eliminated residual spores. We demonstrated that three consecutive uses of an MSC significantly increased the risk of transmission to other fish when compared to the use of BTs or only one spawning event in an MSC (both p < 0.0001). Vertical transmission was not detected with any method. Disinfection with ∼100 ppm bleach soak (pH ∼7.0), 75 ppm Wescodyne soak, and 175 ppm Wescodyne Plus spray was 100% effective in eliminating spores from the MSCs. Disinfection of MSCs before spawning did not decrease P. neurophilia transmission when infected fish remained present in the breeding population. Researchers should avoid using endemically infected fish in MSCs to minimize transmission of pathogens within their colonies.
Embryo surface disinfection is utilized in aquaculture to decrease the risk of pathogen introduction into established colonies. Zebrafish embryos are commonly disinfected with unbuffered sodium hypochlorite at 25-50 ppm for 10 min with or without concurrent treatment with chemicals, including pronase (Pron), sodium thiosulfate, and/or methylene blue; however, the impact of these chemicals on embryo survival and development has not been evaluated. In this study, AB and casper embryos were exposed to disinfection protocols that used Pron, sodium thiosulfate, and/or methylene blue (given alone, in various combinations, or all three combined) with 50 and 100 ppm sodium hypochlorite performed 6 and 24 h postfertilization (HPF). All groups were evaluated for survival, hatching, and malformations at 5 days postfertilization. Maximal survival (69%-97%) and hatching rates (66%-94%) were generally observed with sodium hypochlorite disinfection followed by exposure to both Pron and sodium thiosulfate and maintenance in standard embryo medium without methylene blue. Methylene blue had variable effects on survival and hatching. Higher survival and hatching rates were seen in AB embryos disinfected at 6 HPF and casper embryos disinfected at 24 HPF. Susceptibility to sodium hypochlorite toxicity differed by strain, emphasizing the need to test disinfection protocols on small embryo cohorts.
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