International survey on the use and welfare of zebrafish Danio rerio in research

Identification of Individual Zebrafish (Danio rerio): A Refined Protocol for VIE Tagging Whilst Considering Animal Welfare and the Principles of the 3Rs

In aquatic ecology, studies have commonly employed a tagging technique known as visible implant elastomer (VIE). This method has not been widely adopted by the zebrafish research community and also lacks refinement with regard to animal welfare. The current paper introduces a new VIE tagging protocol, with the aim of improving existing tagging techniques by placing particular emphasis on the Three Rs. To improve animal welfare and fish survival, we added the use of an analgesic compound (lidocaine) through the marking procedure, followed by after-treatment with antiseptics (melaleuca, aloe vera, and PVP-I as active ingredients) to improve tissue regeneration and healing. The newly improved protocol has been quantitatively evaluated on different populations and age groups of zebrafish. This study will be useful to the scientific zebrafish community and to the wider field including biologist and aquarists, especially in consideration of animal welfare, where tagging techniques are considered as a potential noxious stimulus for fish.

Social Preference Tests in Zebrafish: A Systematic Review

The use of animal models in biology research continues to be necessary for the development of new technologies and medicines, and therefore crucial for enhancing human and animal health. In this context, the need to ensure the compliance of research with the principles Replacement, Reduction and Refinement (the 3 Rs), which underpin the ethical and human approach to husbandry and experimental design, has become a central issue. The zebrafish (Danio rerio) is becoming a widely used model in the field of behavioral neuroscience. In particular, studying zebrafish social preference, by observing how an individual fish interacts with conspecifics, may offer insights into several neuropsychiatric and neurodevelopmental disorders. The main aim of this review is to summarize principal factors affecting zebrafish behavior during social preference tests. We identified three categories of social research using zebrafish: studies carried out in untreated wild-type zebrafish, in pharmacologically treated wild-type zebrafish, and in genetically engineered fish. We suggest guidelines for standardizing social preference testing in the zebrafish model. The main advances gleaned from zebrafish social behavior testing are discussed, together with the relevance of this method to scientific research, including the study of behavioral disorders in humans. The authors stress the importance of adopting an ethical approach that considers the welfare of animals involved in experimental procedures. Ensuring a high standard of animal welfare is not only good for the animals, but also enhances the quality of our science.

MS-222 induces biochemical and transcriptional changes related to oxidative stress, cell proliferation and apoptosis in zebrafish embryos

MS-222, the most widely used anaesthetic in fish, has been shown to induce embryotoxic effects in zebrafish. However, the underlying molecular effects are still elusive. This study aimed to investigate the effects of MS-222 exposure during early developmental stages by evaluating biochemical and molecular changes. Embryos were exposed to 50, 100 or 150 mg L^-1 MS-222 for 20 min at one of three developmental stages (256-cell, 50% epiboly, or 1-4 somite stage) and oxidative-stress, cell proliferation and apoptosis-related parameters were determined at two time-points (8 and 26 hpf). Following exposure during the 256-cell stage, the biochemical redox balance was not affected. The genes associated with glutathione homeostasis (gstpi and gclc) were affected at 8 hpf, while genes associated with apoptosis (casp3a and casp6) and cellular proliferation (pcna) were found affected at 26 hpf. An inverted U-shaped response was observed at 8 hpf for catalase activity. After exposure at the 50% epiboly stage, the gclc gene associated with oxidative stress was found upregulated at 8 hpf, while gstpi was downregulated and casp6 was upregulated later on, coinciding with a decrease in glutathione peroxidase (GPx) activity and a non-monotonic elevation of protein carbonyls and casp3a. Additionally, MS-222 treated embryos showed a decrease in DCF-staining at 26 hpf. When exposure was performed at the 1-4 somite stage, a similar DCF-staining pattern was observed. The activity of GPx was also affected whereas RT-qPCR showed that caspase transcripts were dose-dependently increased (casp3a, casp6 and casp9). The pcna mRNA levels were also found to be upregulated while gclc was changed by MS-222. These results highlight the impact of MS-222 on zebrafish embryo development and its interference with the antioxidant, cell proliferation and cellular death systems by mechanisms still to be explained; however, the outcomes point to the Erk/Nrf2 signalling pathway as a target candidate.

Anticipatory plastic response of the cellular immune system in the face of future injury: chronic high perceived predation risk induces lymphocytosis in a cichlid fish

Vertebrate cellular immunity displays substantial variation among taxa and environments. Hematological parameters such as white blood-cell counts have emerged as a valuable tool to understand this variation by assessing the immunological status of individuals. These tools have long revealed that vertebrate cellular immune systems are highly plastic and respond to injury and infection. However, cellular immune systems may also be able to anticipate a high risk of injury from environmental cues (e.g., predation-related cues) and respond plastically ahead of time. We studied white blood-cell (leukocyte) profiles in African cichlids Pelvicachromis taeniatus that were raised for 4 years under different levels of perceived predation risk. In a split-clutch design, we raised fish from hatching onwards under chronic exposure to either conspecific alarm cues (communicating high predation risk) or a distilled water control treatment. Differential blood analysis revealed that alarm cue-exposed fish had twice as many lymphocytes in peripheral blood as did controls, a condition called lymphocytosis. The presence of a higher number of lymphocytes makes the cellular immune response more potent, which accelerates the removal of invading foreign antigens from the bloodstream, and, therefore, may be putatively beneficial in the face of injury. This observed lymphocytosis after long-term exposure to conspecific alarm cues constitutes first evidence for an anticipatory and adaptive plastic response of the cellular immune system to future immunological challenges.

Skin swabbing is a refined technique to collect DNA from model fish species

Model fish species such as sticklebacks and zebrafish are frequently used in studies that require DNA to be collected from live animals. This is typically achieved by fin clipping, a procedure that is simple and reliable to perform but that can harm fish. An alternative procedure to sample DNA involves swabbing the skin to collect mucus and epithelial cells. Although swabbing appears to be less invasive than fin clipping, it still requires fish to be netted, held in air and handled—procedures that can cause stress. In this study we combine behavioural and physiological analyses to investigate changes in gene expression, behaviour and welfare after fin clipping and swabbing. Swabbing led to a smaller change in cortisol release and behaviour on the first day of analysis compared to fin clipping. It also led to less variability in data suggesting that fewer animals need to be measured after using this technique. However, swabbing triggered some longer term changes in zebrafish behaviour suggesting a delayed response to sample collection. Skin swabbing does not require the use of anaesthetics and triggers fewer changes in behaviour and physiology than fin clipping. It is therefore a more refined technique for DNA collection with the potential to improve fish health and welfare.

Evaluation of the Adverse Effects of Chronic Exposure to Donepezil (An Acetylcholinesterase Inhibitor) in Adult Zebrafish by Behavioral and Biochemical Assessments

Donepezil (DPZ) is an acetylcholinesterase inhibitor used for the clinical treatment of mild cognitive impairment. However, DPZ has been reported to have adverse effects, including causing abnormal cardiac rhythm, insomnia, vomiting, and muscle cramps. However, the existence of these effects in subjects without Dementia is unknown. In this study, we use zebrafish to conduct a deeper analysis of the potential adverse effects of DPZ on the short-term memory and behaviors of normal zebrafish by performing multiple behavioral and biochemical assays. Adult zebrafish were exposed to 1 ppm and 2.5 ppm of DPZ. From the results, DPZ caused a slight improvement in the short-term memory of zebrafish and induced significant elevation in aggressiveness, while the novel tank and shoaling tests revealed anxiolytic-like behavior to be caused by DPZ. Furthermore, zebrafish circadian locomotor activity displayed a higher reduction of locomotion and abnormal movement orientation in both low- and high-dose groups, compared to the control group. Biomarker assays revealed that these alterations were associated with an elevation of oxytocin and a reduction of cortisol levels in the brain. Moreover, the significant increases in reactive oxygen species (ROS) and malondialdehyde (MDA) levels in muscle tissue suggest DPZ exposure induced muscle tissue oxidative stress and muscle weakness, which may underlie the locomotor activity impairment. In conclusion, we show, for the first time, that chronic waterborne exposure to DPZ can severely induce adverse effects on normal zebrafish in a dose-dependent manner. These unexpected adverse effects on behavioral alteration should be carefully addressed in future studies considering DPZ conducted on zebrafish or other animals.

Fast, easy and early (larval) identification of transparent mutant zebrafish using standard fluorescence microscopy

The availability of transparent zebrafish mutants (either TraNac: tra ^b6/b6; nac ^w2/w2 or casper: roy ^a9/a9; nac ^w2/w2 ) for live imaging studies together with the ease of generating transgenic lines are two of the strengths of the zebrafish model organism. The fact that transparent casper ( roy ^a9/a9;nac ^w2/w2) and silver nacre ( nac ^w2/w2) mutants are indistinguishable by eye at early stages (1-5 days post-fertilization; dpf) means many fish must be raised and later culled if they are not transparent. To identify translucent mutants early and easily at the early larval stage (≤5 dpf) before they are classified as protected animals, we developed a simple screening method using standard fluorescence microscopy. We estimate that this procedure could annually save 60,000 animals worldwide.

The Stability and Efficacy of Tricaine Methanesulfonate (MS222) Solution After Long-Term Storage

Tricaine methanesulfonate (MS222) is widely used for the anesthesia and euthanasia of laboratory zebrafish. Fresh solutions have been recommended for each use; however, researchers often mix and store concentrated stock solutions for convenience and to reduce occupational exposure and environmental waste. While this is common practice, published guidelines are often inconsistent. Thus, the objective of this study was to evaluate the stability and anesthetic efficacy of MS222 after long-term storage and to develop specific storage parameters. Stock solutions (100 mg/mL MS222) were mixed and stored in amber jars at 4 °C and -20 °C for 2- and 6-mo. Stability of the solutions was analyzed using liquid chromatography-ion trap mass spectrometry and compared with fresh MS222. Fifty adult (30 male, 20 female) wildtype AB zebrafish (Danio rerio) were randomly anesthetized with 150 mg/L of one of the following MS222 solutions to evaluate anesthetic efficacy: 1) freshly prepared (0m); 2) 2 mo at 4 °C (2m4); 3) 2 mo at -20 °C (2m-20); 4) 6 mo at 4 °C (6m4); 5) 6 mo at -20 °C (6m-20). Time to cessation of swimming, loss of equilibrium, lack of response to von Frey (VF) stimulation, return of equilibrium, and resumption of swimming were compared between groups. Two fish from each group were euthanized at 24-h and 2-wk after anesthesia, and histopathology was performed. All solutions were determined to be stable under all storage conditions. No clinically significant differences were observed between the fresh and stored stock groups during anesthetic testing. No evidence of anesthetic-related histologic changes were noted in the gills, skin, kidneys, muscle, and central nervous system. Hepatic megalocytosis and a reduction in hepatic vacuolation were seen to varying degrees across all groups, but did not follow a treatment-related trend. Therefore, 100 mg/mL solutions of MS222 can be stored in amber jars at 4 °C or -20 °C for 6 mo and still used to effectively anesthetize zebrafish.

Vascular Damage in Obesity and Diabetes: Highlighting Links Between Endothelial Dysfunction and Metabolic Disease in Zebrafish and Man

Endothelial dysfunction is an initial pathophysiological mechanism of vascular damage and is further recognized as an independent predictor of negative prognosis in diabetes-induced micro- and macrovascular complications. Insight into the capability of zebrafish to model metabolic disease like obesity and type II diabetes has increased and new evidence on the induction of vascular pathologies in zebrafish through metabolic disease is available. Here, we raise the question, if zebrafish can be utilized to study the initial impairments of vascular complications in metabolic disorders. In this review, we focus on the advances made to develop models of obesity and type II diabetes in zebrafish, discuss the key points and characteristics of these models, while highlighting the available information linked to the development of endothelial dysfunction in zebrafish and man. We show that larval and adult zebrafish develop metabolic dysregulation in the settings of obesity and diabetes, exhibiting pathophysiological mechanisms, which mimic the human condition. The most important genes related to endothelial dysfunction are present in zebrafish and further display similar functions as in mammals. Several suggested contributors to endothelial dysfunction found in these models, namely hyperinsulinaemia, hyperglycaemia, hyperlipidaemia and hyperleptinaemia are highlighted and the available data from zebrafish are summarised. Many underlying processes of endothelial dysfunction in obesity and diabetes are fundamentally present in zebrafish and provide ground for the assumption, that zebrafish can develop endothelial dysfunction. Conservation of basic biological mechanisms is established for zebrafish, but focused investigation on the subject is now needed as validation and particularly more research is necessary to understand the differences between zebrafish and man. The available data demonstrate the relevance of zebrafish as a model for metabolic disease and their ability to become a proponent for the investigation of vascular damage in the settings of obesity and diabetes.

Dietary and Pharmacological Interventions That Inhibit Mammalian Target of Rapamycin Activity Alter the Brain Expression Levels of Neurogenic and Glial Markers in an Age-and Treatment-Dependent Manner

Intermittent fasting (IF) and its mimetic, rapamycin extend lifespan and healthspan through mechanisms that are not fully understood. We investigated different short-term durations of IF and rapamycin on cellular and molecular changes in the brains of young (6-10 months) and old (26-31 months) zebrafish. Interestingly, our results showed that IF significantly lowered glucose levels while increasing DCAMKL1 in both young and old animals. This proliferative effect of IF was supported by the upregulation of foxm1 transcript in old animals. Rapamycin did not change glucose levels in young and old animals but had differential effects depending on age. In young zebrafish, proliferating cell nuclear antigen and the LC3-II/LC3-I ratio was decreased, whereas glial fibrillary acidic protein and gephyrin were decreased in old animals. The changes in proliferative markers and a marker of autophagic flux suggest an age-dependent interplay between autophagy and cell proliferation. Additionally, changes in glia and inhibitory tone suggest a suppressive effect on neuroinflammation but may push the brain toward a more excitable state. Mammalian target of rapamycin (mTOR) activity in the brain following the IF and rapamycin treatment was differentially regulated by age. Interestingly, rapamycin inhibited mTOR more potently in young animals than IF. Principal component analysis supported our conclusion that the regulatory effects of IF and rapamycin were age-specific, since we observed different patterns in the expression levels and clustering of young and old animals. Taken together, our results suggest that even a short-term duration of IF and rapamycin have significant effects in the brain at young and old ages, and that these are age and treatment dependent.

A 13-plex of tetra- and penta-STRs to identify zebrafish

The zebrafish species Danio rerio has become one of the major vertebrate model organisms used in biomedical research. However, there are aspects of the model that need to be improved. One of these is the ability to identify individual fish and fish lines by DNA profiling. Although many dinucleotide short tandem repeat (diSTR) markers are available for this and similar purposes, they have certain disadvantages such as an excessive polymerase slippage ("stutter") that causes difficulties in automated genotyping and cross-laboratory comparisons. Here we report on the development of a 13-plex of tetranucleotide and pentanucleotide STRs (tetraSTRs and pentaSTRs, respectively) that have low stutter. The system uses an inexpensive universal primer labelling system, which can easily be converted to a direct labeling system if desired. This 13-plex was examined in three zebrafish lines (NHGRI-1, kca33Tg, and kca66Tg, originally obtained from ZIRC). The average observed heterozygosity (Ho) and expected heterozygosity (He) in these highly inbred lines were 0.291 and 0.359, respectively, which is very similar to what has been found with diSTRs. The probability of identity (PI) for all fish tested was 2.1 × 10^-5 and the PI for siblings (PIsib) was 6.4 × 10^-3, as calculated by the Genalex package. Ninety percent of the fish tested were correctly identified with their respective strains. It is also demonstrated that this panel can be used to confirm doubled-haploid cell lines. This multiplex should find multiple uses for improving the accuracy and reproducibility of studies using the zebrafish model.

Effects of chronic prazosin, an alpha-1 adrenergic antagonist, on anxiety-like behavior and cortisol levels in a chronic unpredictable stress model in zebrafish (Danio rerio)

Post-traumatic stress disorder (PTSD) is often associated with significant neuroendocrine dysfunction and a variety of other symptoms. Today, there are limited efficacious treatment options for PTSD, none of which directly target the dysfunction observed with the hypothalamic-pituitary-adrenal (HPA) axis. The development of new pharmacological treatments is expensive and time consuming; thus, there is utility in repurposing compounds already approved for use in other conditions. One medication in particular that has shown promise for the alleviation of PTSD symptoms is prazosin, an alpha-1 adrenergic receptor antagonist used to treat hypertension. While there have been many studies indicating the efficacy of prazosin in the treatment of PTSD symptoms, no studies fully elucidate mechanisms elicited by this treatment, nor is it clear if prazosin normalizes neuroendocrine dysfunction associated with trauma exposure. The use of zebrafish (Danio rerio) has been growing in popularity, in part, due to the homology of the stress response system with mammals. In this study, the zebrafish model was utilized to determine behavioral and biological changes induced by chronic unpredictable stress (CUS) and how these effects could be modulated by chronic prazosin treatment. The results indicated that 7d of CUS increased anxiety-like behavior in the novel tank test and decreased basal levels of cortisol. Chronic (7d) prazosin treatment decreased anxiety-like behaviors overall but did not appear to affect CUS-induced changes in behavior and basal cortisol levels. This suggests that the clinical effectiveness of prazosin may not normalize dysregulated stress responses prevalent in many patients with PTSD, but that prazosin-induced relief from anxiety in stress-related conditions may involve an alternative mechanism other than by normalizing neuroendocrine dysfunction.

"But It's Just a Fish": Understanding the Challenges of Applying the 3Rs in Laboratory Aquariums in the UK

Adopting a social science perspective and qualitative methodology on the problem of laboratory fish welfare, this paper examines some underlying social factors and drivers that influence thinking, priorities and implementation of fish welfare initiatives and the 3Rs (Replacement, Reduction and Refinement) for fish. Drawing on original qualitative interviews with stakeholders, animal technologists and scientists who work with fish-especially zebrafish-to illustrate the case, this paper explores some key social factors influencing the take up of the 3Rs in this context. Our findings suggest the relevance of factors including ambient cultural perceptions of fish, disagreements about the evidence on fish pain and suffering, the discourse of regulators, and the experiences of scientists and animal technologists who develop and put the 3Rs into practice. The discussion is focused on the UK context, although the main themes will be pertinent around the world.

Shade as enrichment: testing preferences for shelter in two model fish species

We compared preferences shown by zebrafish Danio rerio and three-spined stickleback Gasterosteus aculeatus for shelter provided by above-tank shade and artificial plants. Zebrafish showed no preference for either shelter, whereas sticklebacks showed a preference for both shelter types over open areas and for shade over plants. Our results suggest shade may be used as enrichment for captive fish and re-emphasise the importance of species-specific welfare considerations.

Zebrafish: Housing and husbandry recommendations

This article provides recommendations for the care of laboratory zebrafish (Danio rerio) as part of the further implementation of Annex A to the European Convention on the protection of vertebrate animals used for experimental and other scientific purposes, EU Commission Recommendation 2007/526/EC and the fulfilment of Article 33 of EU Directive 2010/63, both concerning the housing and care of experimental animals. The recommendations provide guidance on best practices and ranges of husbandry parameters within which zebrafish welfare, as well as reproducibility of experimental procedures, are assured.

Husbandry procedures found today in zebrafish facilities are numerous. While the vast majority of these practices are perfectly acceptable in terms of zebrafish physiology and welfare, the reproducibility of experimental results could be improved by further standardisation of husbandry procedures and exchange of husbandry information between laboratories. Standardisation protocols providing ranges of husbandry parameters are likely to be more successful and appropriate than the implementation of a set of fixed guidance values neglecting the empirically successful daily routines of many facilities and will better reflect the wide range of environmental parameters that characterise the natural habitats occupied by zebrafish.

A joint working group on zebrafish housing and husbandry recommendations, with members of the European Society for Fish Models in Biology and Medicine (EUFishBioMed) and of the Federation of European Laboratory Animal Science Associations (FELASA) has been given a mandate to provide guidelines based on a FELASA list of parameters, ‘Terms of Reference’.

A Semi-Automatic Dispenser for Solid and Liquid Food in Aquatic Facilities

We present a novel, low-footprint and low-cost semi-automatic system for delivering solid and liquid food to zebrafish, and more generally to aquatic animals raised in racks of tanks. It is composed of a portable main module equipped with a contactless reader that adjusts the quantity to deliver for each tank, and either a solid food module or a liquid food module. Solid food comprises virtually any kind of dry powder or grains below 2 mm in diameter, and, for liquid-mediated food, brine shrimps (Artemia salina) and rotifers (Rotifera) have been successfully tested. Real-world testing, feedback, and validation have been performed in a zebrafish facility for several months. In comparison with manual feeding this system mitigates the appearance of musculoskeletal disorders among regularly-feeding staff, and let operators observe the animals' behavior instead of being focused on quantities to deliver. We also tested the accuracy of both humans and our dispenser and found that the semi-automatic system is much more reliable, with respectively 7-fold and 84-fold drops in standard deviation for solid and liquid food.

Clove Oil and AQUI-S Efficacy for Zebrafish Embryo, Larva, and Adult Anesthesia

Since the use of the zebrafish Danio rerio genetic model organism within the scientific research community continues to grow rapidly, continued procedural refinement to support high-quality, reproducible research and improve animal welfare remains an important focus. As such, anesthesia remains one of the most frequent procedures conducted. Here, we compared the effectiveness of clove oil (active ingredient eugenol) and AQUI-S (active ingredient iso-eugenol) with the currently most commonly used tricaine/MS-222 (ethyl 3-aminobenzoate methanesulfonate) and benzocaine anesthesia. We focused on embryos (1 day postfertilization), larvae (5 days postfertilization), and adults (9-11 months) and for the first time used exposure times that are the most relevant in research settings by using zebrafish as a genetic model system. For each age, tricaine and benzocaine achieved the most reproducible, robust anesthesia with the quickest induction and recovery. For some experimental procedures, specific clove oil concentrations in embryos and larvae may represent suitable alternatives. Although different aquatic species at specific ages respond differentially to these agents, the systematic study of comparable effective dosages for procedures most commonly employed represent an important step toward refinement.

Ethical considerations in fish research

Fishes are used in a wide range of scientific studies, from conservation research with potential benefits to the species used to biomedical research with potential human benefits. Fish research can take place in both laboratories and field environments and methods used represent a continuum from non-invasive observations, handling, through to experimental manipulation. While some countries have legislation or guidance regarding the use of fish in research, many do not and there exists a diversity of scientific opinions on the sentience of fish and how we determine welfare. Nevertheless, there is a growing pressure on the scientific community to take more responsibility for the animals they work with through maximising the benefits of their research to humans or animals while minimising welfare or survival costs to their study animals. In this review, we focus primarily on the refinement of common methods used in fish research based on emerging knowledge with the aim of improving the welfare of fish used in scientific studies. We consider the use of anaesthetics and analgesics and how we mark individuals for identification purposes. We highlight the main ethical concerns facing researchers in both laboratory and field environments and identify areas that need urgent future research. We hope that this review will help inform those who wish to refine their ethical practices and stimulate thought among fish researchers for further avenues of refinement. Improved ethics and welfare of fishes will inevitably lead to increased scientific rigour and is in the best interests of both fishes and scientists.

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.

Increasing the reliability and reproducibility of aquatic ecotoxicology: Learn lessons from aquaculture research

Regulatory ecotoxicology highly relies on aquatic toxicity studies carried out under controlled conditions. Researchers recently expressed increasing concern about their possible lack of repeatability/reproducibility in many cases. Poor experimental designs, inappropriate statistics and lack of accurate reporting are often pointed out. However, I believe that there is also insufficient attention paid to the various experimental conditions under which fish studies are conducted. These conditions encompass numerous factors (temperature, photoperiod, food, stressors…) which modulate fish response to chemicals. Their effects are poorly studied in ecotoxicology but have been investigated for decades in aquaculture research. It is therefore proposed herein to consider experimental ecotoxicology from an aquaculture perspective. An overview of modulating factors and plausible associated experimental flaws is presented, with emphasis to fish health, growth and reproduction which are the most common regulatory endpoints. Photoperiod and temperature mainly determine growth/reproductive status for which fish also have species and stage-specific nutritional requirements. Stressors, sex ratio, density, water quality and factorial interactions may induce experimental bias. Modulating factors can strongly limit findings applicability and might explain the lack of reproducibility in some cases. Aquaculture knowledge/experience can already allow avoiding some experimental flaws (e.g., stress) while further research is warranted for some other aspects (e.g., nutrition). Detailed reporting of fish husbandry and experimental conditions is of utmost importance for study quality assessment.

Is Heightened-Shoaling a Good Candidate for Positive Emotional Behavior in Zebrafish?

Simple Summary

Despite increasing interest in fish welfare, we still know very little about positive emotions in fish. This study had two aims: (1) to characterize a previously undescribed social behavior in zebrafish, “heightened-shoaling”, and (2) to evaluate whether heightened-shoaling may be a good candidate for future research into positive emotional behavior in zebrafish. Observing six groups of zebrafish housed in 110 L tanks furnished with a sloping gravel substrate, rocks, and artificial plants (10 fish/tank), we found that heightened-shoaling is marked by tight group cohesion, high behavioral synchrony (all fish engaging in the same behaviors at the same time), and low agonism. Episodes of heightened-shoaling occurred in all six groups, but rarely at the same time (only once out of 31 episodes), suggesting that the onset of heightened-shoaling is driven by internal group dynamics rather than external influences. Heightened-shoaling also appeared to be self-reinforcing as it had sustained durations—typically lasting for over 7 min and sometimes lasting for nearly half-an-hour. Collectively, these results are similar to the patterns that typify positive emotional behavior in other animals, for example, social grooming and social play. As the first description of heightened-shoaling, this research extends our knowledge of the range of zebrafish social dynamics and suggests a promising area for future research on positive emotions in fish.

Abstract

Zebrafish, a highly-social species of freshwater fish, are widely studied across many fields of laboratory science including developmental biology, neuroscience, and genomics. Nevertheless, as standard housing for zebrafish typically consists of small and simplistic environments, less is known about their social behavioral repertoire in more naturalistic settings. In particular, spontaneously occurring, socio-positive affiliative behaviors (e.g., social coordination and cohesion) that may be indicative of positive emotional experiences have rarely been reported or studied deliberately in zebrafish. Housing adult zebrafish (10 fish/tank) in large semi-natural tanks (110 L; n = 6) with sloping gravel substrate, rocks, and artificial plants, we observed a previously undescribed behavior: Distinct periods of spontaneous, synchronized, compact aggregations, what we call “heightened-shoaling”. This project aimed to quantify the characteristics of this distinctive behavior and compare parameters of heightened-shoaling to baseline periods (normal behavior) and pre-feed periods (feed-anticipatory behavior). First, across 4 days, we selected video-clips (100 s each) from within (i) instances of heightened-shoaling (n = 9), (ii) baseline periods (n = 18), and (iii) pre-feed periods (n = 18). For each of these video clips, we scan sampled every 10 s to determine fish orientations and location within the tank and agonistic behavior. Next, we used an all-occurrence sampling method to record the timing and duration of all episodes of heightened-shoaling behavior when tank-lights were on (8:00 h to 18:00 h) across 10 days. From the scan-sampling data, we found that compared to baseline periods, heightened-shoaling was characterized by increased shoal cohesion (p < 0.0001), increased adherence to the horizontal plane (p < 0.0001), decreased agonism (p < 0.0001), and no diving behavior (lower positions within the water column signal negative effect in zebrafish, p > 0.1). From the all-occurrence sampling data, we found 31 episodes of heightened-shoaling with instances observed in all six tanks and only a single case in which heightened-shoaling occurred in two tanks at the same time. The median episode duration was 7.6 min (Range 1.3–28.6). As the first systematic description of heightened-shoaling behavior, this research contributes to our knowledge of the range of zebrafish social dynamics living in naturalistic environments. Moreover, as a spontaneously occurring, protracted, affiliative behavior, heightened-shoaling appears to be a good candidate for future research into positive emotional behavior in zebrafish.

Can simple tank changes benefit the welfare of laboratory zebrafish Danio rerio?

This study examined the effects of simple changes in the tank environment on the wellbeing of laboratory-maintained zebrafish Danio rerio. Groups of D. rerio were either housed in stable environments (where they were maintained in the same tanks throughout the study) or in environments subject to change (where they were periodically moved to novel but identical tanks) and the effects of these treatments on morphometry, reproductive success and aggressive behaviour assessed. No effect of simple tank changes was found on body condition, reproductive output or aggression, for the periods of time studied, indicating that more complex scenarios in housing tank conditions are required for significant welfare benefits for captive D. rerio.

Report of Workshop on Euthanasia for Zebrafish-A Matter of Welfare and Science

The increasing importance of zebrafish as a biomedical model organism is reflected by the steadily growing number of publications and laboratories working with this species. Regulatory recommendations for euthanasia as issued in Directive 2010/63/EU are, however, based on experience with fish species used for food production and do not take the small size and specific physiology of zebrafish into account. Consequently, the currently recommended methods of euthanasia in the Directive 2010/63/EU are either not applicable or may interfere with research goals. An international workshop was held in Karlsruhe, Germany, March 9, 2017, to discuss and propose alternative methods for euthanasia of zebrafish. The aim was to identify methods that adequately address the physiology of zebrafish and its use as a biomedical research model, follow the principles of the 3Rs (Replacement, Reduction, and Refinement) in animal experimentation and consider animal welfare during anesthesia and euthanasia. The results of the workshop are summarized here in the form of a white paper.

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.