Toxicity of chlorine to zebrafish embryos

Review of Pseudoloma neurophilia (Microsporidia): A common neural parasite of laboratory zebrafish (Danio rerio)

Zebrafish (Danio rerio) is now the second most used animal model in biomedical research. As with other vertebrate models, underlying diseases and infections often impact research. Beyond mortality and morbidity, these conditions can compromise research end points by producing nonprotocol induced variation within experiments. Pseudoloma neurophilia, a microsporidium that targets the central nervous system, is the most frequently diagnosed pathogen in zebrafish facilities. The parasite undergoes direct, horizontal transmission within populations, and is also maternally transmitted with spores in ovarian fluid and occasionally within eggs. This transmission explains the wide distribution among research laboratories as new lines are generally introduced as embryos. The infection is chronic, and fish apparently never recover following the initial infection. However, most fish do not exhibit outward clinical signs. Histologically, the parasite occurs as aggregates of spores throughout the midbrain and spinal cord and extends to nerve roots. It often elicits meninxitis, myositis, and myodegeneration when it infects the muscle. There are currently no described therapies for the parasite, thus the infection is best avoided by screening with PCR-based tests and removal of infected fish from a facility. Examples of research impacts include reduced fecundity, behavioral changes, transcriptome alterations, and autofluorescent lesions.

Interwoven processes in fish development: microbial community succession and immune maturation

Fishes are hosts for many microorganisms that provide them with beneficial effects on growth, immune system development, nutrition and protection against pathogens. In order to avoid spreading of infectious diseases in aquaculture, prevention includes vaccinations and routine disinfection of eggs and equipment, while curative treatments consist in the administration of antibiotics. Vaccination processes can stress the fish and require substantial farmer's investment. Additionally, disinfection and antibiotics are not specific, and while they may be effective in the short term, they have major drawbacks in the long term. Indeed, they eliminate beneficial bacteria which are useful for the host and promote the raising of antibiotic resistance in beneficial, commensal but also in pathogenic bacterial strains. Numerous publications highlight the importance that plays the diversified microbial community colonizing fish (i.e., microbiota) in the development, health and ultimately survival of their host. This review targets the current knowledge on the bidirectional communication between the microbiota and the fish immune system during fish development. It explores the extent of this mutualistic relationship: on one hand, the effect that microbes exert on the immune system ontogeny of fishes, and on the other hand, the impact of critical steps in immune system development on the microbial recruitment and succession throughout their life. We will first describe the immune system and its ontogeny and gene expression steps in the immune system development of fishes. Secondly, the plurality of the microbiotas (depending on host organism, organ, and development stage) will be reviewed. Then, a description of the constant interactions between microbiota and immune system throughout the fish's life stages will be discussed. Healthy microbiotas allow immune system maturation and modulation of inflammation, both of which contribute to immune homeostasis. Thus, immune equilibrium is closely linked to microbiota stability and to the stages of microbial community succession during the host development. We will provide examples from several fish species and describe more extensively the mechanisms occurring in zebrafish model because immune system ontogeny is much more finely described for this species, thanks to the many existing zebrafish mutants which allow more precise investigations. We will conclude on how the conceptual framework associated to the research on the immune system will benefit from considering the relations between microbiota and immune system maturation. More precisely, the development of active tolerance of the microbiota from the earliest stages of life enables the sustainable establishment of a complex healthy microbial community in the adult host. Establishing a balanced host-microbiota interaction avoids triggering deleterious inflammation, and maintains immunological and microbiological homeostasis.

Trihydroxy piperlongumine protects aluminium induced neurotoxicity in zebrafish: Behavioral and biochemical approach

Aluminium (Al) is proven to be a potent environmental neurotoxin involved in progressive neurodegeneration. Al primarily induces oxidative stress by free radical generation in the brain, followed by neuronal apoptosis. Antioxidants are promising therapeutic options for Al toxicity. Piperlongumine is traditionally long known for its medicinal properties. Therefore, the present study has been designed to explore the antioxidant role of trihydroxy piperlongumine (THPL) against Al-induced neurotoxicity in the zebrafish model. Zebrafish exposed to AlCl₃ exhibited higher oxidative stress and altered locomotion. Adult fish displayed anxiety comorbid with depression phenotype. THPL increases antioxidant enzyme activity by quenching Al-induced free radicals and lipid peroxidation, thus minimizing oxidative damage in the brain. THPL rescues behavior deficits and improves anxiety-like phenotype in adult fish. Histological alterations caused by Al were also attenuated on administration with THPL. Results of the study demonstrate the neuroprotective role of THPL against Al-induced oxidative damage and anxiety, which could be exploited as a psychopharmacological drug.

Gurung D, Smit H. Environmental factors affecting water mites (Acari: Hydrachnidia) assemblage in streams, Mangde Chhu basin, central Bhutan

Water mites were sampled from 15 tributary streams of Mangde Chhu river in Zhemgang and Trongsa districts, Central Bhutan in pre-monsoon (April–May) and post-monsoon (October–November) of 2021. A total of 802 individuals were collected belonging to seven families and 15 genera. The accumulation curve suggests that the sampling efforts were adequate to give a proper overview of genera composition for elevations 500–2,700 m. Eleven genera—Aturus, Kongsbergia, Woolastookia, Atractides, Hygrobates, Lebertia, Piona, Sperchonopsis, Monatractides, Pseudotorrenticola and Testudacarus—and five families—Aturidae, Hygrobatidae, Lebertiidae, Pionidae, and Protziinae—are new records for Bhutan. Independent sample t-tests of genera richness (t, (26) = 0.244, p = 0.809); genera evenness (t, (26) = 0.735, p = 0.469); Shannon diversity index (t, (26) = 0.315, p = 0.755) and dominance (t, (26) = -0.335, p = 0.741) showed no significant differences between pre- and post-monsoon assemblages. Species abundance was also not significantly different (t, (28) = -0.976, p = 0.330). Principal component analysis indicated that the diversity of water mites is negatively associated with several environmental variables including chloride (r = -0.617), ammonia (r = -0.603), magnesium hardness (r = -0.649), total hardness (r = -0.509), temperature (r = -0.556), salinity (r = -0.553), total dissolved solids (r = -0.509) and electrical conductivity (r = -0.464). Diversity was positively correlated with altitude, mainly caused by the higher Palaearctic genera diversity. Similarly, Pearson’s correlation test showed that there was significant negative correlation between mite abundance and the water physio-chemical parameters salinity (r = -0.574, p = 0.032), electrical conductivity (r = -0.536, p = 0.048), total dissolved solids (r = -0.534, p = 0.049), total hardness (r = -0.621, p = 0.018), and chloride concentration (r = -0.545, p = 0.036), indicating sensitivity of water mites to pollution.

Evaluation of Media Conductivity and a Combination of Iodine and Sodium Hypochlorite Surface Disinfection on Zebrafish (Danio rerio) Embryo Viability and Morphology

Embryo surface disinfection in either an iodine or sodium hypochlorite (NaOCl) solution is commonly performed on imported zebrafish embryos to decrease pathogen introduction into a facility. The impact of the consecutive use of these disinfectants and the conductivity of the culture media on embryo survival and development post-disinfection have not been evaluated. Iodine (12.5-25 ppm) is effective at eliminating several Mycobacterium species, whereas NaOCl (50-100 ppm) reduces the number of viable Pseudoloma neurophilia spores. Casper and T5D (tropical 5D wild type) embryos reared in media of differing conductivities (0-10, 100-200, 750-950, and 1500-2000 μS) with and without exposure to NaOCl 100 ppm at 6 h post-fertilization were evaluated for survival, hatching success, and morphological defects at 5 days post-fertilization. Additionally, the consecutive use of iodine (12.5 ppm for 2 min) followed by NaOCl (75 or 100 ppm for 10 min), as well as the inverse, was evaluated. Embryo survival was not impacted by embryo rearing media alone; however, survival significantly decreased when embryos were disinfected with 100 ppm NaOCl in media with a conductivity >750-950 μS. Iodine (12 ppm) and NaOCl (75 ppm) used sequentially resulted in >50% survival, whereas the use of 100 ppm NaOCl resulted in high levels of embryo mortality.

Dietary Perfluorohexanoic Acid (PFHxA) Exposures in Juvenile Zebrafish Produce Subtle Behavioral Effects across Generations

Ubiquitous anthropogenic contaminants of concern, per- and polyfluoroalkyl substances (PFAS) are frequently detected in the environment and human populations around the world. Diet is a predominate route of human exposure, and PFAS are frequently measured in food. Manufacturing trends have shifted from legacy PFAS to shorter-chain alternatives that are suggested to be safer, such as perfluorohexanoic acid (PFHxA). However, the current amount of data to support safety assessments of these alternatives is not yet sufficient. The present study investigated the effects of a 42-day dietary exposure to 1, 10, or 100 ng/g PFHxA in juvenile zebrafish. The zebrafish model was leveraged to interrogate morphometrics, fecundity, and numerous behavior endpoints across multiple generations. Dietary PFHxA exposure did not result in measurable body burden and did not affect growth, fecundity, adult social perception behavior, or associative learning. PFHxA exposure did induce abnormal adult anxiety behaviors in the F0 generation that persisted transgenerationally in the F1 and F2. Abnormal larval and juvenile behavior was observed in the F1 generation, but not in the F2. PFHxA juvenile dietary exposure induced subtle and multigenerational behavior effects that warrant further investigation of this and other alternative short-chain PFAS.

Fluorescent probe for the detection of hypochlorous acid in water samples and cell models

Hypochlorous acid (HClO) is a special kind of reactive oxygen species, which plays an important role in resisting pathogen invasion and maintaining cell redox balance and other physiological processes. In addition, HClO is commonly used in daily life as a bleaching and disinfectant agent. Its excessive use can also lead to death of water animals and serious respiratory and skin diseases in humans. Therefore, it is of great significance to develop a quick and convenient tool for detecting HClO in the environment and organisms. In this paper, we utilize the specific reaction of HClO with dimethylthiocarbamate to develop a novel naphthalene derivative fluorescent probe (BNA-HClO), it was designed and synthesized by using 6-(2-benzothiazolyl)-2-naphthol as the fluorophore and N,N-dimethylthiocarbamate as the recognition group. BNA-HClO shows large fluorescence enhancement (374-fold), high sensitivity (a detection limit of 37.56 nM), rapid response (<30 s), strong anti-interference ability and good specificity in vitro. Based on the outstanding in vitro sensing capability of BNA-HClO, it has been successfully used to detect spiked HClO in tap water, medical wastewater and fetal bovine serum with good recovery. BNA-HClO has also been successfully used as a portable test strip for the in situ semi-quantitative detection of HClO in tap water solutions. In addition, BNA-HClO can successfully enable the detection and imaging of exogenous and endogenous HClO in living cells. This work provides a simple and effective tool for the detection and imaging of HClO in environmental and biological systems, and provides some theoretical guidance for future exploration of biological and pathological studies related to HClO.

Testing Alternative Surface Disinfection Agents for Zebrafish (Danio rerio) Embryos

Pathogen transmission into zebrafish colonies is controlled through vigilant biosecurity practices. One such practice is embryo surface disinfection, which often uses sodium hypochlorite. However, if sodium hypochlorite is used at an inappropriate pH, concentration, or exposure time, zebrafish embryos can experience significant mortality and morbidity. Reagent-grade sodium hypochlorite is often used for embryo surface disinfection because commercial-grade sodium hypochlorite has additional ingredients that may have deleterious effects on the embryo. In addition, chlorine dioxide and the combination of sodium chloride and potassium peroxymonosulfate (SCPP) are effective equipment disinfectants; however, the effects of these chemical agents on zebrafish embryos during surface disinfection are unknown. In this study, we exposed strain 5D zebrafish embryos (ages, 6 and 24 h postfertilization) to 4 chlorine-containing agents (reagent-grade sodium hypochlorite [bleach], commercial-grade sodium hypochlorite [bleach], SCPP, and chlorine dioxide) at either 50- or 100- ppm for 5 or 10 min. All groups were evaluated at 5 d postfertilization for survival, hatching rate, and morphologic defect rate. The experimental group with the highest survival and hatching rates and the lowest morphologic defect rate was the 24-h postfertilization embryos exposed to 50 ppm SCPP for 5 min. The survival, hatching rate, and defect rate did not differ significantly among age-matched controls; however, the hatching rate after exposure to 50 ppm SCPP was significantly higher than that of embryos exposed to 50 ppm reagent-grade sodium hypochlorite for 5 min (100% compared with 23% respectively). SCPP solution may provide an alternative surface disinfectant for zebrafish embryos because it maximizes survival and hatching rates and minimizes morphologic defect rates. However, in vivo efficacy against common zebrafish pathogens requires further testing. Use of chlorine dioxide at 50 ppm or greater is not recommended for zebrafish embryo surface disinfection due to significant mortality among 6 and 24 h postfertilization embryos.

Exposure to aluminium causes behavioural alterations and oxidative stress in the brain of adult zebrafish

Aluminium (Al) water pollution is an increasing environmental problem. Accordingly, this study aimed to find out more about its toxic effects on aquatic organisms. Adult zebrafish were exposed to 11 mg/L of Al and the behavioural responses and its correlation with brain oxidative stress, antioxidant-defences, changes in metabolism and neurotransmission were assessed at 10, 15 and 20 days of exposure. The behavioural and locomotory responses, suggest an increase in the anxiety state, especially observed in animals exposed to Al for 15 days. The reactive oxygen species increased in a time-dependent trend, while the oxidative damage varied over exposure time. The activity of antioxidant enzymes, as superoxide dismutase, glutathione peroxidase and glutathione S-transferases, and the metallothioneins levels increased after short-term exposures and tended to decrease or stabilize at longer times. The results contribute to understand the toxic mechanisms activated by Al highlighting correlations like behavioural disorders and oxidative state.

Impact of Pronase, Sodium Thiosulfate, and Methylene Blue Combinations on Development and Survival of Sodium Hypochlorite Surface-Disinfected Zebrafish (Danio rerio) Embryos

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.

Viability of Pseudocapillaria tomentosa Eggs Exposed to Heat, Ultraviolet Light, Chlorine, Iodine, and Desiccation

Pseudocapillaria tomentosa is an important pathogen in zebrafish facilities. We investigated heat, ultraviolet (UV) light, chlorine, iodine, and dessciation for killing the parasite's eggs. Eggs released with feces larvate in about 5-10 days, and treatments were evaluated by exposing fresh eggs and subsequently comparing larvation to untreated eggs as an indication of survival. Collectively, untreated eggs in all trials showed high levels of survival. Eggs were exposed to elevated temperatures (40°C, 45°C and 50°C) for 1, 8, or 24 h, which resulted in substantial reduction in viability of eggs. UV radiation was effective, with no larvation at 50-300 mWs/cm² and <2% at 20 mWs/cm². Three chlorine products (JT Baker, Clorox^®, and Bi-Mart) were tested at 25, 50, 100, 500, and 3,000 ppm (pH 7.0-7.3) with 10 min exposure. All were effective at 500 or 1,000 ppm. There was variability between three products and trials at lower concentrations, but overall chlorine was not very effective at 25-100 ppm except for Bi-Mart brand at 100 ppm. Povidone-iodine was not effective at 25 or 50 ppm for 10 min, but was effective at 200 ppm for 1 h. Desiccation was effective, and no eggs larvated after 2 h drying.

Zebrafish Embryo Disinfection with Povidone-Iodine: Evaluating an Alternative to Chlorine Bleach

Mycobacteriosis is a common bacterial infection in laboratory zebrafish caused by several different species and strains of Mycobacterium, including both rapid and slow growers. One control measure used to prevent mycobacterial spread within and between facilities is surface disinfection of eggs. Recent studies have highlighted the effectiveness of povidone-iodine (PVPI) on preventing propagation of Mycobacterium spp. found in zebrafish colonies. We evaluated the effect of disinfection using 12.5-50 ppm PVPI (unbuffered and buffered) on zebrafish exposed at 6 or 24 h postfertilization (hpf) to determine if this treatment is suitable for use in research zebrafish. Our results show that 6 hpf embryos are less sensitive to treatment as fewer effects on mortality, developmental delay, and deformity were observed. We also found that buffered PVPI treatment results in a greater knockdown of Mycobacterium chelonae and Mycobacterium marinum, as well as results in decreased harmful effects on embryos. Treatments of shorter (2 min vs. 5 min) duration were also more effective at killing mycobacteria in addition to resulting in fewer effects on embryo health. In addition, we compared the efficacy of a rinsing regimen to rinsing and disinfecting. Based on the findings of this study, we recommend disinfecting embryos for 2 min with buffered PVPI at 12.5-25 ppm.

Strategies to Mitigate a Mycobacterium marinum Outbreak in a Zebrafish Research Facility

In 2011, the zebrafish research facility at the University of Oregon experienced an outbreak of Mycobacterium marinum that affected both research fish and facility staff. A thorough review of risks to personnel, the zebrafish veterinary care program, and zebrafish husbandry procedures at the research facility followed. In the years since 2011, changes have been implemented throughout the research facility to protect the personnel, the fish colony, and ultimately the continued success of the zebrafish model research program. In this study, we present the history of the outbreak, the changes we implemented, and recommendations to mitigate pathogen outbreaks in zebrafish research facilities.

Transmission of Pseudoloma neurophilia in Laboratory Zebrafish (Danio rerio) When Using Mass Spawning Chambers and Recommendations for Chamber Disinfection

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.

Breeding Zebrafish: A Review of Different Methods and a Discussion on Standardization

In recent years, a rapidly increasing number of scientific papers have been published that utilize zebrafish (Danio rerio) as an alternative model organism in the study of a wide range of biological phenomena from cancer to behavior. This is, in large part, due to the prolific nature, relative ease of maintenance, and sufficiently high genetic homology of zebrafish to humans. With the surge of zebrafish use in animal research, the variations in methodologies of breeding and husbandry of this species have also increased. Investigators usually focus on the development and implementation of rigorous laboratory control that is specific to their studies. We suggest that the same scrutiny and attention may be required for the methods of breeding and housing of zebrafish. This article reviews a variety of zebrafish husbandry and breeding techniques and conditions employed around the world. It discusses factors ranging from numerous aspects of rearing/housing conditions through the sex ratio of the breeding group to the composition of the diet of zebrafish that may vary across laboratories. It provides some feedback on the potential pros and cons of the different methods. It argues that there is a substantial need for systematic analysis of these methods, that is, the effects of environmental factors on zebrafish health and breeding. It also discusses the question as to whether some degree of standardization of these methods is needed to enhance cross-laboratory comparability of results.

Comparison of Antemortem and Environmental Samples for Zebrafish Health Monitoring and Quarantine

Molecular diagnostic assays offer both exquisite sensitivity and the ability to test a wide variety of sample types. Various types of environmental sample, such as detritus and concentrated water, might provide a useful adjunct to sentinels in routine zebrafish health monitoring. Similarly, antemortem sampling would be advantageous for expediting zebrafish quarantine, without euthanasia of valuable fish. We evaluated the detection of Mycobacterium chelonae, M. fortuitum, M. peregrinum, Pseudocapillaria tomentosa, and Pseudoloma neurophilia in zebrafish, detritus, pooled feces, and filter membranes after filtration of 1000-, 500-, and 150-mL water samples by real-time PCR analysis. Sensitivity varied according to sample type and pathogen, and environmental sampling was significantly more sensitive than zebrafish sampling for detecting Mycobacterium spp. but not for Pseudocapillaria neurophilia or Pseudoloma tomentosa. The results of these experiments provide strong evidence of the utility of multiple sample types for detecting pathogens according to each pathogen's life cycle and ecological niche within zebrafish systems. In a separate experiment, zebrafish subclinically infected with M. chelonae, M. marinum, Pleistophora hyphessobryconis, Pseudocapillaria tomentosa, or Pseudoloma neurophilia were pair-spawned and individually tested with subsets of embryos from each clutch that received no rinse, a fluidizing rinse, or were surface-disinfected with sodium hypochlorite. Frequently, one or both parents were subclinically infected with pathogen(s) that were not detected in any embryo subset. Therefore, negative results from embryo samples may not reflect the health status of the parent zebrafish.

A method for collecting eggs of Pseudocapillaria tomentosa (Nematoda: Capillariidae) from zebrafish Danio rerio and efficacy of heat and chlorine for killing the nematode's eggs

Pseudocapillaria tomentosa is a common pathogen of zebrafish (Danio rerio) in research facilities. We developed a method to collect and concentrate the nematode eggs using a modified sugar centrifugation method and documented their normal development. Embryonating stages with blastomere formation followed by elongation of the embryo prior to larva formation cumulated in developed larvae inside the eggs and hatching after 5-10 day. We then evaluated the efficacy of heat and chlorine to kill them based on a larva development assay. Eggs were exposed to 40, 50, 60 °C for 30 min and 1 h. Chlorine treatment was performed at 100, 250, 500, 1000, 3000 and 6000 ppm for 10 min. Samples exposed to 40 °C for 30 min or 1 h showed incidences of larvated eggs similar to controls. In contrast, no larvation occurred with eggs exposed to either 50 or 60 °C for 30 min or 1 h. Remarkably, in repeated assays, samples exposed to low doses of chlorine (100, 250, 500 and 1000 ppm for 10 min) showed significantly higher incidence of larvation than controls. Eggs treated with 3000 ppm for 10 min did not develop larvae, and no eggs were found after 6000 ppm treatment.

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

The presence of subclinical infection or clinical disease in laboratory zebrafish may have a significant impact on research results, animal health and welfare, and transfer of animals between institutions. As use of zebrafish as a model of disease increases, a harmonized method for monitoring and reporting the health status of animals will facilitate the transfer of animals, allow institutions to exclude diseases that may negatively impact their research programs, and improve animal health and welfare. All zebrafish facilities should implement a health monitoring program. In this study, we review important aspects of a health monitoring program, including choice of agents, samples for testing, available testing methodologies, housing and husbandry, cost, test subjects, and a harmonized method for reporting results. Facilities may use these recommendations to implement their own health monitoring program.

Triclosan Exposure Is Associated with Rapid Restructuring of the Microbiome in Adult Zebrafish

Growing evidence indicates that disrupting the microbial community that comprises the intestinal tract, known as the gut microbiome, can contribute to the development or severity of disease. As a result, it is important to discern the agents responsible for microbiome disruption. While animals are frequently exposed to a diverse array of environmental chemicals, little is known about their effects on gut microbiome stability and structure. Here, we demonstrate how zebrafish can be used to glean insight into the effects of environmental chemical exposure on the structure and ecological dynamics of the gut microbiome. Specifically, we exposed forty-five adult zebrafish to triclosan-laden food for four or seven days or a control diet, and analyzed their microbial communities using 16S rRNA amplicon sequencing. Triclosan exposure was associated with rapid shifts in microbiome structure and diversity. We find evidence that several operational taxonomic units (OTUs) associated with the family Enterobacteriaceae appear to be susceptible to triclosan exposure, while OTUs associated with the genus Pseudomonas appeared to be more resilient and resistant to exposure. We also found that triclosan exposure is associated with topological alterations to microbial interaction networks and results in an overall increase in the number of negative interactions per microbe in these networks. Together these data indicate that triclosan exposure results in altered composition and ecological dynamics of microbial communities in the gut. Our work demonstrates that because zebrafish afford rapid and inexpensive interrogation of a large number of individuals, it is a useful experimental system for the discovery of the gut microbiome's interaction with environmental chemicals.

Facility Design and Health Management Program at the Sinnhuber Aquatic Research Laboratory

The number of researchers and institutions moving to the utilization of zebrafish for biomedical research continues to increase because of the recognized advantages of this model. Numerous factors should be considered before building a new or retooling an existing facility. Design decisions will directly impact the management and maintenance costs. We and others have advocated for more rigorous approaches to zebrafish health management to support and protect an increasingly diverse portfolio of important research. The Sinnhuber Aquatic Research Laboratory (SARL) is located ∼3 miles from the main Oregon State University campus in Corvallis, Oregon. This facility supports several research programs that depend heavily on the use of adult, larval, and embryonic zebrafish. The new zebrafish facility of the SARL began operation in 2007 with a commitment to build and manage an efficient facility that diligently protects human and fish health. An important goal was to ensure that the facility was free of Pseudoloma neurophilia (Microsporidia), which is very common in zebrafish research facilities. We recognize that there are certain limitations in space, resources, and financial support that are institution dependent, but in this article, we describe the steps taken to build and manage an efficient specific pathogen-free facility.

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

Mycobacteriosis is a bacterial disease that is common in captive, wild and research fish. There is no one causative agent of mycobacteriosis, as several strains and species of Mycobacterium have been identified in zebrafish. With increased usage and investment in wild-type and mutant zebrafish strains, considerable value is placed on preserving zebrafish health. One control measure used to prevent mycobacterial spread within and between zebrafish facilities is egg disinfection. Here we investigate the effectiveness of three disinfectants [chlorine bleach, hydrogen peroxide, and povidone-iodine (PVPI)] commonly included in egg disinfection protocols for laboratory fish as well as aquaculture fish and compare the knockdown effect of these treatments on Mycobacterium spp. in vitro. Despite current usage, comparison of these disinfection regimes' abilities to prevent mycobacterial growth has not been tested. We found that the germicidal effect of different disinfectants varies by Mycobacterium spp. Hydrogen peroxide was the least effective disinfectant, followed by unbuffered chlorine bleach, which is commonly used to disinfect embryos in zebrafish facilities. Disinfection with 25ppm PVPI for 5min was very effective, and may be an improved alternative to chlorine bleach for embryo disinfection. Results from this study can be utilized by laboratory fish facilities in order to prevent the spread of mycobacteriosis in research fish.

Biosafe inertization of municipal solid waste incinerator residues by COSMOS technology

Municipal solid waste incinerator (MSWI) residues can generate negative environmental impacts when improperly handled. The COlloidal Silica Medium to Obtain Safe inert (COSMOS) technology represents a new method to stabilize MSWI residues and to produce inert safe material. Here we report the results about aquatic biotoxicity of lixiviated MSWI fly ash and the corresponding inertized COSMOS material using a zebrafish (Danio rerio) embryo toxicity test. Quantitative assessment of waste biotoxicity included evaluation of mortality rate and of different morphological and teratogenous endpoints in zebrafish embryos exposed to tested materials from 3 to 72h post-fertilization. The results demonstrate that lixiviated MSWI fly ash exerts a dose-dependent lethal effect paralleled by dramatic morphological/teratogenous alterations and apoptotic events in the whole embryo body. Similar effects were observed following MSWI fly ash stabilization in classical concrete matrices, demonstrating that the obtained materials are not biologically safe. On the contrary, no significant mortality and developmental defects were observed in zebrafish embryos exposed to COSMOS inert solution. Our results provide the first experimental in vivo evidence that, in contrast with concrete stabilization procedure, COSMOS technology provides a biologically safe inert.