Recommendations for control of pathogens and infectious diseases in fish research facilities

The battle against the introduced pathogenic monogenean Gyrodactylus salaris in Norwegian Atlantic salmon rivers and fish farms

The introduced salmonid ectoparasite Gyrodactylus salaris has been detected on Atlantic salmon in 53 Norwegian rivers and in 39 Norwegian fish farms. In affected rivers, the mortality of Atlantic salmon juveniles is very high, estimated to a mean of 86%. G. salaris has been considered one of the biggest threats to wild Norwegian Atlantic salmon stocks. With various measures, the authorities have reduced the potential for further spread of the parasite to new rivers and fish farms, and G. salaris has been eradicated from 43 rivers and all fish farms. Furthermore, the eradication process is almost completed in five affected rivers located at the Norwegian west coast, while preparations for the eradication in the remaining five rivers in the southeastern part of Norway have begun. The goal of Norwegian management is to eradicate the introduced pathogenic G. salaris strains from all occurrences in Norway. In fish farms, the parasite has been removed by mandatory slaughter of infected fish. In rivers, G. salaris has mostly been removed by killing all the fish hosts with rotenone. The indigenous genetic Atlantic salmon stocks are re-established after eradication of the parasite. New methods are developed using chemicals that kill the parasite without killing fish in the rivers. Norwegian authorities have so far used more than NOK 1.5 billion on research, monitoring and combating G. salaris. However, the benefits are considered many times greater than the spending. Without control measures, G. salaris would likely have spread to new Atlantic salmon rivers where the same catastrophic outcome had to be expected. The Norwegian authorities seem to meet the goal in their long-term work to halt the spread of G. salaris and to eradicate the parasite in affected rivers.

In vitro immune-depression and anti-inflammatory activities of cantharidin on gilthead seabream (Sparus aurata) leucocytes activated by λ-carrageenan

Cantharidin is a natural compound with known therapeutic applications in humans. The aim of this study was to investigate the in vitro effects of cantharidin on gilthead seabream (Sparus aurata) head kidney leucocytes (HKL) stimulated with λ-carrageenan. HKLs were incubated for 24 h with cantharidin (0, 2.5 and 5 μg mL-1) and λ-carrageenan (0 and 1000 μg mL-1). The results showed that HKL viability only decreased by 15.2% after incubated with 5 μg mL-1 of cantharidin and λ-carrageenan. Cantharidin increased the peroxidase activity of HKLs only when incubated in combination with λ-carrageenan. Besides this, cantharidin inhibited the respiratory burst and phagocytic activities. Furthermore, cantharidin induced morphological changes in HKLs (apoptotic and vacuolization signs) that were enhanced when incubated with λ-carrageenan. Considering the analysis of the selected gene expression studied in HKLs [NF-κB subunits (rela, relb, crel, nfkb1, nfkb2), proinflammatory cytokines (il1b, tnfa), anti-inflammatory cytokines (il10, tgfb) and caspases (casp1, casp3, casp8, casp9)], although λ-carrageenan up-regulated the expression of the proinflammatory gene il1b, λ-carrageenan and cantharidin down-regulated its expression in HKLs. In addition, cantharidin up-regulated casp3 and casp9 expression. The casp3 and casp9 gene expression was down-regulated while casp1 gene expression was up-regulated in HKLs incubated with both cantharidin and λ-carrageenan. All the effects of cantharidin are related to its inhibitory effect on protein phosphatases, which induce apoptosis at long exposure times, and minimize the effects of λ-carrageenan. The present results provide detailed insight into the immune-depressive and anti-inflammatory properties of cantharidin on immune cells, which could be of interest to the aquaculture sector.

Development of Immersion and Oral Bivalent Nanovaccines for Streptococcosis and Columnaris Disease Prevention in Fry and Fingerling Asian Seabass (Lates calcarifer) Nursery Farms

In the present study, chitosan-based bivalent nanovaccines of S. iniae and F. covae were administered by immersion vaccination at 30 and 40 days after hatching (DAH), and the third vaccination was orally administered by feeding at 50 DAH. ELISA revealed that the levels of total IgM and specific IgM to S. iniae and F. covae were significantly elevated in all vaccinated groups at 10, 20, and 30 days after vaccination (DAV). A qRT-PCR analysis of immune-related genes revealed significantly higher IgT expression in the vaccinated groups compared to the control group, as revealed by 44-100-fold changes in the vaccinated groups compared to the control (p < 0.001) at every tested time point after vaccination. All vaccinated groups expressed IgM, MHCIIα, and TCRα at significantly higher levels than the control group at 10 and/or 20 DAV (p < 0.05). In the S. iniae challenge tests, the survival of vaccinated groups ranged from 62.15 ± 2.11 to 75.70 ± 3.36%, which significantly differed from that of the control group (44.44 ± 1.92%). Similarly, all vaccinated groups showed higher survival rates of 68.89 ± 3.85 to 77.78 ± 5.09% during F. covae challenge than the control groups (50.00 ± 3.33%) (p < 0.05).

A FELASA Working Group Survey on Fish Species Used for Research, Methods of Euthanasia, Health Monitoring, and Biosecurity in Europe, North America, and Oceania

Simple Summary

An international survey was conducted regarding species used for research, methods of euthanasia, health monitoring, and biosecurity in fish laboratories. A total of 145 facilities from 23 countries contributed. Over 80 different species were reported to be used for research, of which zebrafish (Danio rerio) was the most common by far. Anesthetic overdose was the preferred method for euthanasia for adults, fry, and larvae not capable of independent feeding. For all developmental stages, the most popular anesthetic compound was tricaine. Around half of the respondents did not perform a completion method to ensure death. One-quarter of the responding facilities did not have a health monitoring system in place. Only a small fraction reported quarantine routines to ensure reliable biological barriers. There was little consensus amongst facilities in how to perform biosecurity measures.

Abstract

An international survey was conducted regarding species used for research, methods of euthanasia, health monitoring, and biosecurity in fish laboratories. A total of 145 facilities from 23 countries contributed. Collectively, over 80 different species (or groups of species) were reported to be used for research, of which zebrafish (Danio rerio) was the most common by far. About half of the participating laboratories used multiple species. Anesthetic overdose was the preferred method for euthanasia for adult, fry (capable of independent feeding), and larval (not capable of independent feeding) fish. For all developmental stages, the most popular anesthetic compound was tricaine (MS-222), a substance associated with distress and aversion in several species. Moreover, around half of the respondents did not perform a completion method to ensure death. One-quarter of the responding facilities did not have a health monitoring system in place. While most respondents had some form of quarantine process for imported fish, only a small fraction reported quarantine routines that ensure reliable biological barriers. Furthermore, less than one in five screened fish for pathogens while in quarantine. In sum, there was little consensus amongst facilities in how to perform biosecurity measures. Regarding euthanasia, health monitoring, and biosecurity processes, there is a need for updated and universal guidelines and for many laboratories to adjust their practices.

Mucoadhesive cationic lipid-based Flavobacterium oreochromis nanoencapsulation enhanced the efficacy of mucoadhesive immersion vaccination against columnaris disease and strengthened immunity in Asian sea bass (Lates calcarifer)

Columnaris is a bacterial disease, found in freshwater fish, caused by Flavobacterium oreochromis. The disease has a devastating impact on a range of cultured and wild freshwater fish species e.g. Lates calcarifer (Asian sea bass), which is a serious economic losses to the freshwater aquaculture in Thailand. The disease can be prevented by an efficacious vaccine, however, no licensed effective vaccine is available to date. Current study was based on the development of a novel mucoadhesive nano-encapsulated vaccine (EncapFlavoNP⁺⁺), where, cationic lipid-based nanoparticles were combined with an antigen obtained from F. oreochromis. Various parameters including transmission electron microscopy (TEM), physiochemical properties; zeta potential, and polydispersity index were determined. The TEM results depicted well-formed circular-shaped nano-encapsulates complexed with cationic lipid surfactants. The average diameter of the molecules was 200 nm, having a zeta potential of 31.82 mV, while, the polydispersity index (PDI) was 0.31. The in vivo study lasted for 8 weeks, the immunologic and protective potentials of the prepared molecules were determined by challenging the fish for 8 weeks. The most effective dilutions of EncapFlavoNP⁺⁺ solution were 1:100 and 1:200, which significantly improved the efficacy of the immunity by increasing the level of antibody specific to F. oreochromis. A trend of upregulation was found in the immune-related genes including immunoglobulin M heavy chain (IgM), major histocompatibility complex class IIα molecules (MHC-IIα), and dendritic cell specific transcript (DCs) in gills, skin, liver, peripheral blood lymphocytes (PBLs), head kidneys, and spleen as compared to the control group (P < 0.05 and P < 0.01). Upon immunization with EncapFlavoNP⁺⁺ solution at the dilution of 1:100 and 1:200, the significant increase in survival rate (SR) and relative percent survival (RPS) were found in fish challenged with virulent F. oreochromis bacterium (SR 72.50% and RPS 62.07) and (SR 65.83% and RPS 52.87), respectively as compared to the control group (P < 0.05). It can be concluded that immunization with EncapFlavoNP⁺⁺ solution has significant immunologic and protective effects against Columnaris disease. Furthermore, the prepared vaccine candidate has more potential as compared to whole-cell immersion vaccination (FK-WC). It can be used on a large scale in the freshwater aquaculture industry to boost immunity against Columnaris disease.

Evaluation of a Recirculating Aquaculture System Research Facility Designed to Address Current Knowledge Needs in Atlantic Salmon Production

A better understanding of recirculating aquaculture system (RAS) biosecurity is crucial for the sustainable and ethical production of Atlantic salmon smolt and post-smolt in these systems. This study described and evaluated the performance of a RAS facility for fish infection research with Atlantic salmon as the main animal model. Fish body weight, length, water quality, and system metrics from five independent experimental trials conducted between September 2020 and July 2021 were used to analyze the variation within and between treatments. Statistical power analysis was performed to determine the minimum number of fish required. The fish parameters variability showed that the inter-class correlation coefficient was on average low (0.1) and that the variation within tanks was larger than the variation between the tanks. The power analysis showed that 15 fish were required to be sampled per tank under these study conditions. Variation of water quality and system management metrics among the five experimental trials was higher compared to the variation within the five experimental trials. Moreover, the variation of the water quality parameters controlled by sensors was relatively low, whereas the parameters depending on biofilter maturation level and performance presented a very high variation. Water exchange rate-dependent quality parameters showed a similar variation value, i.e., nitrate and water turbidity. The established baseline for variability and performance presents an important reference for the design and realization of future experiments in RAS facilities. It is foreseen that the current research facility will develop new knowledge to improve the RAS biosecurity in the Atlantic salmon aquaculture industry.

A Systematic Analysis of Metal and Metalloid Concentrations in Eight Zebrafish Recirculating Water Systems

Metals and metalloids are integral to biological processes and play key roles in physiology and metabolism. Nonetheless, overexposure to some metals or lack of others can lead to serious health consequences. In this study, eight zebrafish facilities collaborated to generate a multielement analysis of their centralized recirculating water systems. We report a first set of average concentrations for 46 elements detected in zebrafish facilities. Our results help to establish an initial baseline for trouble-shooting purposes, and in general for safe ranges of metal concentrations in recirculating water systems, supporting reproducible scientific research outcomes with zebrafish.

Effects of Pseudoloma neurophilia infection on the brain transcriptome in zebrafish (Danio rerio)

Laboratory zebrafish are commonly infected with the intracellular, brain-infecting microsporidian parasite Pseudoloma neurophilia. Chronic P. neurophilia infections induce inflammation in meninges, brain and spinal cord, and have been suggested to affect neural functions since parasite clusters reside inside neurons. However, underlying neural and immunological mechanisms associated with infection have not been explored. Utilizing RNA-sequencing analysis, we found that P. neurophilia infection upregulated 175 and downregulated 45 genes in the zebrafish brain, compared to uninfected controls. Four biological pathways were enriched by the parasite, all of which were associated with immune function. In addition, 14 gene ontology (GO) terms were enriched, eight of which were associated with immune responses and five with circadian rhythm. Surprisingly, no differentially expressed genes or enriched pathways were specific for nervous system function. Upregulated immune-related genes indicate that the host generally show a pro-inflammatory immune response to infection. On the other hand, we found a general downregulation of immune response genes associated with anti-pathogen functions, suggesting an immune evasion strategy by the parasite. The results reported here provide important information on host-parasite interaction and highlight possible pathways for complex effects of parasite infections on zebrafish phenotypes.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Simultaneous Administration of <i>Boesenbergia pandurata</i> Extract and Vaccination to Stimulate Immune Response in Tilapia, <i>Oreochromis niloticus</i>

BACKGROUND AND OBJECTIVE

The use of adjuvants or immunostimulants is often necessary to increase vaccine efficacy, in this study we evaluated the improvement of the immune response in tilapia treated by either oral and immersion administration with vaccine and Boesenbergia pandurata extract (BPE).

MATERIALS AND METHODS

The initial concentration of BPE and the cell density of vaccine were 900 mg L-1 and 104 CFU mL-1 for oral administration while 106 CFU mL-1 for immersion, respectively. The extract and vaccine were mixed homogeneously in a ratio of 1:1. Further, the mixture was supplemented to feed at 1 mL g-1 feed. Tilapia with average initial body weight of 15 g were fed containing vaccine and BPE 3 times a day. The other group of fish was immersed with vaccine and BPE for 20 min. After 7th (d7), 14th (d14) and21th (d21) days of treatment, a challenge test was conducted by intramuscularly injection of 0.1 mL of Aeromonas hydrophila and Pseudomonas fluorescens mixture (1:1) at a density of 105 CFU mL-1. Antibody levels, total white blood cell (WBC) and phagocytic activity (PA) were evaluated to determine the immune improvement of the fish. Furthermore, relative percent survival (RPS) and the survival rate (SR) were evaluated at week 2 and 4 after challenge test.

RESULT

Results indicated that the all parameters of tilapia immune system were increased (p<0.05) after 2-4 weeks of both administration methods. Meanwhile, the efficacy of the vaccine has increased by combining BPE treatment using immersion method better than oral method. The RPS of vaccination plus extract by immersion was 83-100% and by oral administration was 83-87%.

CONCLUSION

The present results implied that B. pandurata extract boost the efficacy of the Pseudomonas sp. vaccine by increasing the immune system and diseases resistance in tilapia.

Probiotic Effects of a Novel Strain, Acinetobacter KU011TH, on the Growth Performance, Immune Responses, and Resistance against Aeromonas hydrophila of Bighead Catfish (Clarias macrocephalus Günther, 1864)

In the present study, the novel probiotic strain Acinetobacter KU011TH with an evident lack of pathogenicity in catfish was experimented. Three practical administration routes, namely, feed additive (FD), water-soluble additive (SOL), and a combination route (FD+SOL), were applied in two sizes of catfish. After 120 days of FD+SOL administration, catfish fingerlings (15 g) exhibited a significant improvement in all tested growth performance parameters. For 15- and 30-day applications at the juvenile stage (150 g), phagocytic activity, phagocytic index, lysozyme activity, respiratory burst activity, alternative complement pathway, and bactericidal activity were significantly increased. Furthermore, probiotic-administered bighead catfish exhibited an upregulated expression of several immune-related genes in tested organs. Significant colonization by Acinetobacter KU011TH in rearing water and on skin and gills was observed among experimental groups. Histological analysis clearly indicated enhanced physical characteristics of skin mucosal immunity in the treated groups. No histopathological changes in the gills, skin, intestine or liver were observed among the fish groups. Interestingly, after challenge with Aeromonas hydrophila, the survival rates of the treated groups were significantly higher than those of the controls. In conclusion, the novel probiont Acinetobacter KU011TH provides a potent strategy for improvement in growth and disease resistance, which is an important steppingstone for sustaining catfish aquaculture.

Source or Sink: Examining the Role of Biofilms in Transmission of Mycobacterium spp. in Laboratory Zebrafish

Zebrafish health is a primary research concern because diseases can have unintended impacts on experimental endpoints. Ideally, research would be conducted using disease-free fish or fish with known disease status. Mycobacteriosis is a common bacterial disease in wild and captive fishes, including zebrafish. Despite its prevalence, the dynamics of transmission and potential sources of mycobacterial infections in zebrafish are only partially understood. One suspected natural infection source is surface biofilms on tanks and other system components. This study investigates the role that tank biofilms play in mycobacteriosis in laboratory zebrafish by evaluating the establishment of biofilms from bacteria shed from fish, and conversely, the acquisition of infections in fish from surface biofilms. We found that zebrafish infected with Mycobacterium chelonae shed bacteria through feces, and bacteria are transmitted to tank biofilms from one to 16 weeks postinfection. We also found that zebrafish acquire M. chelonae infections as soon as 2 weeks when introduced to tanks with established M. chelonae biofilms. The results from this study highlight the role that tank biofilms play as both a reservoir and source of mycobacterial infections in zebrafish. Results support the inclusion of biofilm surveillance and prevention as part of a disease control program in zebrafish research facilities.

Overview of a Disease Outbreak and Introduction of a Step-by-Step Protocol for the Eradication of Mycobacterium haemophilum in a Zebrafish System

In 2017, the zebrafish unit at University of Glasgow experienced a detrimental outbreak of pathogenic bacterium, Mycobacterium haemophilum. The presence of other bacterial species was also confirmed by bacteriology growth in the same unit. The affected individuals composed of a wild-origin parental population sourced from India and their F1 offspring generation. Bacteria were diagnostically confirmed to be present systemically in fish and within the water and biofilm of the recirculating zebrafish system. In the absence of a publicly accessible step-by-step disinfectant protocol for these difficult-to-eliminate pathogens, we devised a successful procedure to eradicate mycobacteria and Aeromonas species after colony removal using Cleanline Chlorine tablets (active ingredient Sodium dichloroisocyanurate) and Virkon Aquatic^®. Postdisinfection diagnostics did not detect pathogens in the system or in the new fish inhabiting the system that were tested. Newly established fish colonies have not shown similar clinical signs or disease-induced mortality in the 1-year period following system disinfection and repopulation. We present a historical background of the bacterial outbreak and a disinfection method which can be replicated in other zebrafish facilities—at small or large scales—for reliable mycobacterium removal. This procedure can be implemented as a disinfection protocol before the introduction of a new fish population to a previously contaminated system.

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.

Antibiotic treatment of zebrafish mycobacteriosis: tolerance and efficacy of treatments with tigecycline and clarithromycin

Zebrafish (Danio rerio) are a popular model organism used in a growing number of research fields. Maintaining healthy, disease-free laboratory fish is important for the integrity of many of these studies. Mycobacteriosis is a chronic bacterial infection caused by several Mycobacterium spp. and is the second most common disease found in laboratory zebrafish. Current mycobacteriosis control measures recommend the removal of infected fish and in severe outbreaks, depopulation. These measures can be effective, but less disruptive measures should be assessed for controlling mycobacteriosis, particularly when valuable and rare lines of fish are affected. Here, the in vivo efficacy of two drug candidates, tigecycline (1 μg g^-1 ) and clarithromycin (4 μg g^-1 ), was tested in adult zebrafish experimentally infected with Mycobacterium chelonae. We assessed both short (14 day)- and long-term (30 day) treatments and evaluated fecundity and pathological endpoints. Fecundity and histology results show that zebrafish tolerated antibiotics. Antibiotic treatments did not significantly impact the prevalence of acid-fast granulomas; however, the severity of infections (acid-fast granuloma intensity) was significantly decreased following treatments.

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.

Implementation of a Zebrafish Health Program in a Research Facility: A 4-Year Retrospective Study

In the past two decades, zebrafish (Danio rerio)-based research has contributed to significant scientific advances. Still, husbandry and health programs did not evolve at the same pace, as evidenced by the absence of general guidelines. Health monitoring is essential to animal welfare, to permit animal exchanges across facilities, to contribute to robust experimental results, and for data reproducibility. In this study, we report a health program implemented in a zebrafish research facility to prevent, monitor, and control pathogen, and disease dissemination. This program includes quarantine, routine health screening of sentinels, and nonroutine screenings of retired animals and sick/moribund individuals. An extensive list of clinical signs, lesions, and pathogens was monitored based on: daily observation of fish, necropsy, histology, and bacterial culture. The results indicate that the combined analysis of sentinels with the evaluation of sick/moribund animals enables a comprehensive description not only of pathogen prevalence but also of clinical and histopathologic lesions of resident animals. The establishment of a quarantine program revealed to be effective in the reduction of Pseudoloma neurophilia frequency in the main aquaria room. Finally, characterization of the colony health status based on this multiapproach program shows a low prevalence of lesions and pathogens in the facility.

Biosecurity and Health Monitoring at the Zebrafish International Resource Center

The Zebrafish International Resource Center (ZIRC) is a repository and distribution center for mutant, transgenic, and wild-type zebrafish. In recent years annual imports of new zebrafish lines to ZIRC have increased tremendously. In addition, after 15 years of research, we have identified some of the most virulent pathogens affecting zebrafish that should be avoided in large production facilities, such as ZIRC. Therefore, while importing a high volume of new lines we prioritize safeguarding the health of our in-house fish colony. Here, we describe the biosecurity and health-monitoring program implemented at ZIRC. This strategy was designed to prevent introduction of new zebrafish pathogens, minimize pathogens already present in the facility, and ensure a healthy zebrafish colony for in-house uses and shipment to customers.

The Vital Relationship Between Nutrition and Health in Zebrafish

In the relatively short span of four decades, the zebrafish (Danio rerio) has emerged as an increasingly important model organism for biomedicine and other scientific disciplines. As the scale and sophistication of zebrafish research expands, so too does the need to develop standards that promote the production and maintenance of healthy animals for experiments. A major, but long overlooked, contributor to fish health is nutrition. Historically, feeding practices for laboratory zebrafish have been designed to promote growth and reproductive function. However, as the field matures, it is becoming increasingly clear that the nutritional goals for these animals should evolve beyond basic production to the maintenance of clinically healthy research subjects. This review outlines weaknesses and limitations of current approaches and provides a justification for the development of defined standardized diets that will strengthen and facilitate the continued growth of the zebrafish model system.

Three-Dimensional Screen: A Comprehensive Approach to the Health Monitoring of Zebrafish

Considering the numbers of zebrafish held in the laboratories, it is relevant to develop some tools to monitor the health of the animals, as well as their biotope. Environmental samples can be used to detect aquatic pathogens. Comprehensive health monitoring would thus seek pathogens in three dimensions of the animals and microbes' habitat: the fish, the sludge, and the water. This three-dimensional approach is called the 3D screen and it introduces some complementary tools to routine sentinel screening. For example, sludge and sump swabs analyses allow an efficient detection of pathogens at a low cost and with a fast turnover. These assays are particularly useful in cases of Pseudocapillaria tomentosa infestation or Mycobacterium haemophilum outbreak. Indeed, such a broader choice of diagnostic tests gives flexibility for the veterinarian to investigate Mycobacterium spp. presence in the water systems and fish colonies. Some other robust additional analysis, like the mortality rate monitoring, quickens the decision-making process. The 3D screen describes how this new toolbox can be used efficiently to monitor laboratory fish health.

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.

Activity of Antibiotics against Mycobacterium Species Commonly Found in Laboratory Zebrafish

The Zebrafish Danio rerio is a popular vertebrate model organism used in a wide range of research fields. Importance is placed on Zebrafish health and the maintenance of disease-free laboratory fish so that experimental studies are not inadvertently affected. Mycobacteriosis, a common infection of laboratory Zebrafish, is caused by several Mycobacterium species. Little is known regarding the potential of antibiotic treatment for Zebrafish mycobacteriosis; however, treatment of infected Zebrafish may be appropriate to maintain valuable strains. Here, we investigated, in vitro, the antibiotic susceptibility of both rapid- and slow-growing isolates of Mycobacterium species from laboratory Zebrafish. Antibiotic testing was carried out using a commercially available 96-well microtiter plate format. Results indicated that some but not all antibiotics tested were effective at inhibiting mycobacterial growth and that susceptibility varied among species and strains. Tigecycline, tobramycin, clarithromycin, and amikacin were most effective at broad inhibition of rapid-growing mycobacteria; whereas, amikacin, clarithromycin, and rifampin were effective at inhibiting all slow-growing M. marinum strains tested. Results support the potential for targeted antibiotic treatment of Zebrafish infected with mycobacteria, but additional testing should be carried out in vivo.

Occurrence of a myxozoan parasite Myxidium streisingeri n. sp. in laboratory zebrafish Danio rerio

Over several years of screening diagnostic cases, the Zebrafish International Resource Center Health Services has encountered a myxozoan parasite of the ducts associated with the kidney in zebrafish, Danio rerio , from an average of 21% of facilities submitting specimens over 5 yr. The parasite is coelozoic and is associated with no appreciable histological changes. Plasmodia bear ovoid spores with 3 sutural ridges. Spores are consistent with the genus Myxidium, but they are distinct from any known species and are thus described as Myxidium streisingeri n. sp. Phylogenetically, this parasite is a member of the polyphyletic urinary bladder clade, which is consistent with the site of infection. The common occurrence of a myxozoan in this closed husbandry system is unexpected because these parasites are known to have complex life cycles, alternating between a vertebrate and invertebrate host. It may be that biofilters provide habitat for suitable invertebrate hosts or perhaps M. streisingeri n. sp. can be transmitted directly. Future control of this parasite in zebrafish research laboratories depends on a better understanding of this life cycle.

Paramecium caudatum enhances transmission and infectivity of Mycobacterium marinum and M. chelonae in zebrafish Danio rerio

Mycobacterial infections in laboratory zebrafish Danio rerio are common and widespread in research colonies. Mycobacteria within free-living amoebae have been shown to be transmission vectors for mycobacteriosis. Paramecium caudatum are commonly used as a first food for zebrafish, and we investigated this ciliate's potential to serve as a vector of Mycobacterium marinum and M. chelonae. The ability of live P. caudatum to transmit these mycobacteria to larval, juvenile and adult zebrafish was evaluated. Infections were defined by histologic observation of granulomas containing acid-fast bacteria in extraintestinal locations. In both experiments, fish fed paramecia containing mycobacteria became infected at a higher incidence than controls. Larvae (exposed at 4 d post hatch) fed paramecia with M. marinum exhibited an incidence of 30% (24/80) and juveniles (exposed at 21 d post hatch) showed 31% incidence (14/45). Adult fish fed a gelatin food matrix containing mycobacteria within paramecia or mycobacteria alone for 2 wk resulted in infections when examined 8 wk after exposure as follows: M. marinum OSU 214 47% (21/45), M. marinum CH 47% (9/19), and M. chelonae 38% (5/13). In contrast, fish feed mycobacteria alone in this diet did not become infected, except for 2 fish (5%) in the M. marinum OSU 214 low-dose group. These results demonstrate that P. caudatum can act as a vector for mycobacteria. This provides a useful animal model for evaluation of natural mycobacterial infections and demonstrates the possibility of mycobacterial transmission in zebrafish facilities via contaminated paramecia cultures.

Edwardsiellosis caused by Edwardsiella ictaluri in laboratory populations of Zebrafish Danio rerio

We report the first cases of Edwardsiella ictaluri causing epizootics in laboratory populations of Zebrafish Danio rerio. Edwardsiella ictaluri is primarily recognized as a disease of catfish species and is known to cause an economically important bacterial disease of farm-raised catfish in the USA and abroad; however, it has been isolated on occasion from 10 other genera of nonictalurid fishes. We isolated E. ictaluri from moribund Zebrafish held in quarantine at two different universities in two states and from a research facility in a third state between February 23 and December 6, 2011. Edwardsiellosis in Zebrafish can be described as a severe systemic disease characterized by tissue necrosis and the presence of large numbers of extracellular and intracellular bacteria, often within macrophages. The kidneys (pronephros and mesonephros), spleen, nares, and forebrain were the most commonly and severely affected tissues. In outbreaks, mortality was acute and numerous fish died over a 1-2 week period. Mortality continued until the majority of the population was lost, at which time the remaining fish were euthanized. In addition to these cases, four cultures of bacteria isolated from Zebrafish by another diagnostic laboratory were submitted to the Louisiana Aquatic Diagnostic Laboratory for identification and were confirmed as E. ictaluri. In total, eight cultures of E. ictaluri from Zebrafish from Louisiana, Massachusetts, Pennsylvania, and Florida were identified. The isolates were confirmed as E. ictaluri by biochemical phenotype, API 20E (bioMérieux), and amplification and sequencing of a portion of the 16S rRNA gene. Edwardsiella ictaluri isolates from Zebrafish are believed to comprise a unique group and were differentiated from catfish isolates by exhibiting weaker motility, autoaggregation in broth, a different plasmid profile (two plasmids of 4.0 and 3.5 kb), a different API 20E code (4204000), and lack of lipopolysaccharide recognition with Mab Ed9.

Viral diseases in zebrafish: what is known and unknown

Naturally occurring viral infections have the potential to introduce confounding variability that leads to invalid and misinterpreted data. Whereas the viral diseases of research rodents are well characterized and closely monitored, no naturally occurring viral infections have been characterized for the laboratory zebrafish (Danio rerio), an increasingly important biomedical research model. Despite the ignorance about naturally occurring zebrafish viruses, zebrafish models are rapidly expanding in areas of biomedical research where the confounding effects of unknown infectious agents present a serious concern. In addition, many zebrafish research colonies remain linked to the ornamental (pet) zebrafish trade, which can contribute to the introduction of new pathogens into research colonies, whereas mice used for research are purpose bred, with no introduction of new mice from the pet industry. Identification, characterization, and monitoring of naturally occurring viruses in zebrafish are crucial to the improvement of zebrafish health, the reduction of unwanted variability, and the continued development of the zebrafish as a model organism. This article addresses the importance of identifying and characterizing the viral diseases of zebrafish as the scope of zebrafish models expands into new research areas and also briefly addresses zebrafish susceptibility to experimental viral infection and the utility of the zebrafish as an infection and immunology model.

Mycobacteriosis in zebrafish colonies

Mycobacteriosis, a chronic bacterial infection, has been associated with severe losses in some zebrafish facilities and low-level mortalities and unknown impacts in others. The occurrence of at least six different described species (Mycobacterium abscessus, M. chelonae, M. fortuitum, M. haemophilum, M. marinum, M. peregrinum) from zebrafish complicates diagnosis and control because each species is unique. As a generalization, mycobacteria are often considered opportunists, but M. haemophilum and M. marinum appear to be more virulent. Background genetics of zebrafish and environmental conditions influence the susceptibility of fish and progression of disease, emphasizing the importance of regular monitoring and good husbandry practices. A combined approach to diagnostics is ultimately the most informative, with histology as a first-level screen, polymerase chain reaction for rapid detection and species identification, and culture for strain differentiation. Occurrence of identical strains of Mycobacterium in both fish and biofilms in zebrafish systems suggests transmission can occur when fish feed on infected tissues or tank detritus containing mycobacteria. Within a facility, good husbandry practices and sentinel programs are essential for minimizing the impacts of mycobacteria. In addition, quarantine and screening of animals coming into a facility is important for eliminating the introduction of the more severe pathogens. Elimination of mycobacteria from an aquatic system is likely not feasible because these species readily establish biofilms on surfaces even in extremely low nutrient conditions. Risks associated with each commonly encountered species need to be identified and informed management plans developed. Basic research on the growth characteristics, disinfection, and pathogenesis of zebrafish mycobacteria is critical moving forward.

Comparison of fixatives and fixation time for PCR detection of Mycobacterium in zebrafish Danio rerio

Mycobacteriosis is a common disease of laboratory zebrafish Danio rerio. Different infection patterns occur in zebrafish depending on mycobacterial species. Mycobacterium marinum and M. haemophilum produce virulent infections associated with high mortality, whereas M. chelonae is more widespread and is not associated with high mortality. Identification of mycobacterial infections to the species level provides important information for making management decisions. Observation of acid-fast bacilli in histological sections or tissue imprints is the most common diagnostic method for mycobacteriosis in fish, but only allows for diagnosis to the genus level. Mycobacterial culture followed by molecular or biochemical identification is the traditional approach, but DNA of diagnostic value can also be retrieved from paraffin blocks. Here we investigated the type of fixative, time in fixative before processing, species of mycobacteria, and severity of infection as parameters to determine whether the hsp gene PCR assay (primer set HS5F/hsp667R) could detect and amplify mycobacterial DNA from paraffin-embedded zebrafish. Whole zebrafish were experimentally infected with either M. chelonae or M. marinum, and then preserved in 10% neutral buffered formalin or Dietrich's fixative for 3, 7, 21, and 45 d. Subsequently, fish were evaluated by hematoxylin and eosin and Fite's acid-fast stains to detect mycobacteria within granulomatous lesions. The PCR assay was quite effective and obtained PCR product from 75 and 88% of the M. chelonae- and M. marinum-infected fish, respectively. Fixative type, time in fixative, and mycobacterial species showed no statistical relationship with the efficacy of the PCR test.

Application of artificial photoperiod in fish: a factor that increases susceptibility to infectious diseases?

This paper describes and evaluates the mortality associated with the potential stressor effect induced by application of artificial photoperiods in rainbow trout (Oncorhynchus mykiss). After application of artificial photoperiods, high mortalities of trout subjected to this management were recorded (36% in LD 14:10 and 25% in LD 24:0) as compared to controls (7%). The recorded signology related to diseased trout included darkening, lethargy and erratic swimming. Among the morphological changes, skin lesions and ulcerative-type necrosis could be observed. Blood tests, histopathology and isolation of pathogens identified as Flavobacterium psychrophilum, associated with Aeromonas, Pseudomonas and Saprolegnia sp., were performed. The application of artificial photoperiods suggests that fish may be more susceptible to opportunistic diseases; thus, it is advisable to emphasize preventive measures in fish subjected to this management.

Aquatic environment, housing, and management in the eighth edition of the Guide for the Care and Use of Laboratory Animals: additional considerations and recommendations

The eighth edition of the Guide for the Care and Use of Laboratory Animals recognizes the widespread use of aquatic and semiaquatic research animals by including, among other references, an entire section on aquatic animals in its chapter on environment, housing, and management. Recognizing the large number of aquatic and semiaquatic species used in research and the inherent diversity in animal needs, the Guide refers the reader to texts and journal reviews for specific recommendations and suggests consultations with persons experienced in caring for aquatic species. Here we present considerations that may add to the basic information presented in the Guide and offer some recommendations that may be useful for aquatic animal model caregivers and researchers.

The challenges of implementing pathogen control strategies for fishes used in biomedical research

Over the past several decades, a number of fish species, including the zebrafish, medaka, and platyfish/swordtail, have become important models for human health and disease. Despite the increasing prevalence of these and other fish species in research, methods for health maintenance and the management of diseases in laboratory populations of these animals are underdeveloped. There is a growing realization that this trend must change, especially as the use of these species expands beyond developmental biology and more towards experimental applications where the presence of underlying disease may affect the physiology animals used in experiments and potentially compromise research results. Therefore, there is a critical need to develop, improve, and implement strategies for managing health and disease in aquatic research facilities. The purpose of this review is to report the proceedings of a workshop entitled "Animal Health and Disease Management in Research Animals" that was recently held at the 5th Aquatic Animal Models for Human Disease in September 2010 at Corvallis, Oregon to discuss the challenges involved with moving the field forward on this front.

Microsporidiosis in zebrafish research facilities

Pseudoloma neurophilia (Microsporidia) is the most common pathogen detected in zebrafish (Danio rerio) from research facilities. The parasite infects the central nervous system and muscle and may be associated with emaciation and skeletal deformities. However, many fish exhibit subclinical infections. Another microsporidium, Pleistophora hyphessobryconis, has recently been detected in a few zebrafish facilities. Here, we review the methods for diagnosis and detection, modes of transmission, and approaches used to control microsporidia in zebrafish, focusing on P. neurophilia. The parasite can be readily transmitted by feeding spores or infected tissues, and we show that cohabitation with infected fish is also an effective means of transmission. Spores are released from live fish in various manners, including through the urine, feces, and sex products during spawning. Indeed, P. neurophilia infects both the eggs and ovarian tissues, where we found concentrations ranging from 12,000 to 88,000 spores per ovary. Hence, various lines of evidence support the conclusion that maternal transmission is a route of infection: spores are numerous in ovaries and developing follicles in infected females, spores are present in spawned eggs and water from spawning tanks based on polymerase chain reaction tests, and larvae are very susceptible to the infection. Furthermore, egg surface disinfectants presently used in zebrafish laboratories are ineffective against microsporidian spores. At this time, the most effective method for prevention of these parasites is avoidance.

Development of a sensitive assay for the detection of Pseudoloma neurophilia in laboratory populations of the zebrafish Danio rerio

The zebrafish Danio rerio is an increasingly important biological model in many areas of research. Due to the potential for non-protocol-induced variation, diseases of zebrafish, especially those resulting in chronic, sub-lethal infections, are of great concern. The microsporidium Pseudoloma neurophilia is a common parasite of laboratory zebrafish. Current methods for detection of this parasite require lethal sampling of fish, which is often undesirable with poorly spawning mutant lines and small populations. We present here an improved molecular-based diagnostic assay using real-time polymerase chain reaction (PCR), and including sonication treatment prior to DNA extraction. Comparisons of several DNA extraction methods were performed to determine the method providing the maximum sensitivity. Sonication was found to be the most effective method for disrupting spores. Compared to previously published data on PCR-based assay using a dilution experiment, sensitivity is increased. This shows that our assay, which includes sonication, is capable of detecting parasite DNA at 1 log higher dilution than the conventional PCR-based assay, which does not include sonication. Furthermore, we demonstrate the application of this method to testing of water, eggs, and sperm, providing a potential non-lethal method for detection of this parasite in zebrafish colonies with a sensitivity of 10 spores 1(-1) of water, 2 spores per spiked egg sample, and 10 spores microl(-1) of spiked sperm sample.

Transmission, diagnosis, and recommendations for control of Pseudoloma neurophilia infections in laboratory zebrafish (Danio rerio) facilities

The microsporidium Pseudoloma neurophilia represents a considerable challenge for laboratory zebrafish (Danio rerio) facilities. In 2010, P. neurophilia infections were diagnosed in zebrafish from 74% of the facilities that submitted fish to the Zebrafish International Resource Center (ZIRC) pathology service, and this organism remains the most commonly diagnosed pathogen in submitted fish. Accordingly, many of the ZIRC pathology service consultations deal with control and prevention of microsporidiosis. Here we describe observations and experiments performed at the ZIRC elucidating aspects of P. neurophilia transmission in zebrafish colonies. We then review current knowledge about P. neurophilia transmission and diagnosis. Considering this information, we present recommendations for control of P. neurophilia in zebrafish facilities.

Development and maintenance of a specific pathogen-free (SPF) zebrafish research facility for Pseudoloma neurophilia

Pseudoloma neurophilia (Microsporidia) is very common in zebrafish Danio rerio research facilities. A new zebrafish facility has been established at the Sinnhuber Aquatic Resource Laboratory (SARL), Oregon State University, Corvallis, OR, U.S.A., and this was an opportunity to establish a specific pathogen-free (SPF) colony of zebrafish for this microsporidium. Progeny from 9 zebrafish lines (n=2203) were initially transferred to the SARL facility in 2007 following PCR screening of broodstock and a subpopulation of progeny (258 of 1000 fish from each family). Screening of fish for P. neurophilia within the facility was conducted as follows: (1) Moribund or dead fish were examined by histology. (2) Each line was regenerated on a 4 mo rotation, and a subsample of each of these major propagations (60 fry, in pools of 10) was PCR-screened at 10 d post hatch. (3) Adult fish (approximately 1 yr old) from each line were euthanized; 20 fish were examined by histology and the brains of another 60 fish (in pools of 5) were screened by PCR. (4) This screening was replicated on sentinel fish held in 4 tanks receiving effluent water from all tanks in the facility (20 fish per tank). (5) Four-month old fish (n=760) from a toxicology study conducted within the laboratory were examined by histology. To date, we have evaluated 2800 fish by PCR and 1222 fish by histology without detecting P. neurophilia. Thus, we have established 9 lines of zebrafish SPF for P. neurophilia. However, 26 fish exhibited mycobacteriosis, with acid-fast bacteria present in tissue sections, and 49 other fish had incidental lesions.

Advances in zebrafish husbandry and management

The zebrafish has emerged over the past several decades to become a mainstream animal model. While the growth of the use of the fish in basic biomedical research has been characterized by innovation, the methods and tools for fish husbandry, management, and care have been slow to evolve beyond those conceived during the initial establishment of the model system. While these approaches and technologies have certainly served the purposes of the field, they must now be improved to better match the widening scope and scale of research being done in fish. Such advances are made possible by applying new scientific information to the development of more sophisticated approaches for fish husbandry and management, and by considering the lessons learned during the establishment of the rodent model system. This review highlights the recent progress made in various areas of fish husbandry and management and points out new directions for further improvements.

Using amphibians in laboratory studies: precautions against the emerging infectious disease chytridiomycosis

The African clawed frog Xenopus laevis is by far the most widely used amphibian species in laboratories. In the wild, X. laevis is an asymptomatic carrier of an emerging infectious disease called chytridiomycosis. The vector is the chytrid fungus Batrachochytrium dendrobatidis (Bd), which has devastating effects on wild amphibian populations around the world. The impact of Bd on the metabolism of X. laevis has not been comprehended yet. However, even if asymptomatic, an infection is likely to affect the individual's physiology, immunology, development, reproduction and overall response to stress from a purely medical point of view, which will introduce noise and therefore increase variance within experimental groups of X. laevis. This could have implications on the scientific results from studies using this species. Here, we review the current knowledge on treatments of infected amphibians and propose a hygiene protocol adapted to laboratory populations and amphibian husbandry. Following the presented sanitation guidelines could further prevent the spread of Bd and probably of other amphibian pathogens. The sanitation guidelines will help to reduce the impact of amphibian husbandry on natural populations and must be considered a crucial contribution to amphibian conservation, as today 32% of all amphibians are considered threatened.

Pleistophora hyphessobryconis (Microsporidia) infecting zebrafish Danio rerio in research facilities

Zebrafish Danio rerio are important models for biomedical research, and thus, there is an increased concern about diseases afflicting them. Here we describe infections by Pleistophora hyphessobryconis (Microsporidia) in zebrafish from 3 laboratories. As reported in other aquarium fishes, affected zebrafish exhibited massive infections in the skeletal muscle, with no involvement of smooth or cardiac muscle. In addition, numerous spores within macrophages were observed in the visceral organs, including the ovaries. Transmission studies and ribosomal RNA (rRNA) gene sequence comparisons confirmed that the parasite from zebrafish was P. hyphessobryconis as described from neon tetra Paracheirodon innesi. Ten 15 d old zebrafish were exposed to P. hyphessobryconis collected from 1 infected neon tetra, and 7 of 10 fish became infected. Comparison of P. hyphessobryconis small subunit rRNA gene sequence from neon tetra with that obtained from zebrafish was nearly identical, with < 1% difference. Given the severity of infections, P. hyphessobryconis should be added to the list of pathogens that should be avoided in zebrafish research facilities, and it would be prudent to avoid mixing zebrafish used in research with other aquarium fishes.

Pseudoloma neurophilia infections in zebrafish Danio rerio: effects of stress on survival, growth, and reproduction

Pseudoloma neurophilia (Microsporidia) is a common disease of zebrafish Danio rerio, including those used as research models. We conducted a study comprised of 4 separate experiments to determine the effects of husbandry stress on preexisting and experimental P. neurophilia infections and the subsequent effects on survival, infection onset and intensity, fish growth, and reproduction. In fish (AB strain) with preexisting infections, stress or feeding cortisol significantly increased mortality over 7 wk compared to no stress or cortisol treatment. In contrast, no mortality was observed in fish (TL strain) experimentally exposed to P. neurophilia over 10 wk. A third experiment involved experimental exposure of AB fish to P. neurophilia and exposure to crowding and handling stressors. No mortality was associated with P. neurophilia regardless of stress treatment over a period of 20 wk. However, the onset of infection occurred sooner in stress-treated fish. Stress significantly increased the mean intensity of infection (described as xenoma area/spinal cord area in histological sections) at Week 20 post-exposure (PE). In fish with preexisting infections, myositis was significantly greater in stressed and cortisol-treated fish than those not stressed. With experimental exposure of AB fish, stressed and infected groups weighed significantly less than the control group at Week 20 PE. Regarding fecundity, the number of larvae hatched at 5 d post fertilization was negatively associated with mean infection intensity among P. neurophilia-infected and stressed AB fish. These experiments are the first to show empirically that P. neurophilia can be associated with reduced weight and fecundity, and that stress can exacerbate the severity of the infection.

Whole-body cortisol response of zebrafish to acute net handling stress

Zebrafish, Danio rerio, are frequently handled during husbandry and experimental procedures in the laboratory, yet little is known about the physiological responses to such stressors. We measured the whole-body cortisol levels of adult zebrafish subjected to net stress and air exposure at intervals over a 24 h period; cortisol recovered to near control levels by about 1 h post-net-stress (PNS). We then measured cortisol at frequent intervals over a 1 h period. Cortisol levels were more than 2-fold higher in net stressed fish at 3 min PNS and continued to increase peaking at 15 min PNS, when cortisol levels were 6-fold greater than the control cortisol. Mean cortisol declined from 15 to 60 min PNS, and at 60 min, net-stressed cortisol was similar to control cortisol. Because the age of fish differed between studies, we examined resting cortisol levels of fish of different ages (3, 7, 13, and 19 months). The resting cortisol values among tanks with the same age fish differed significantly but there was no clear effect of age. Our study is the first to report the response and recovery of cortisol after net handling for laboratory-reared zebrafish.