Evaluation of anaesthetic protocols for laboratory adult zebrafish (Danio rerio)

Assessment of the effect of tricaine (MS-222)-induced anesthesia on brain-wide neuronal activity of zebrafish (Danio rerio) larvae

Fast and effective anesthesia is the key for refining many invasive procedures in fish and gaining reliable data. For fish as for all vertebrates, it is also required by European law to reduce pain, suffering, and distress to the unavoidable minimum in husbandry and experiments. The most often used substance to induce anesthesia in zebrafish is tricaine (MS-222). When properly prepared and dosed, tricaine causes rapid loss of mobility, balance and reaction to touch. These signs are interpreted as a stage of deep anesthesia although its effects on the central nervous system have not convincingly been shown. Therefore, it might be possible that tricaine first acts only on the periphery, resulting in a paralyzed instead of an anesthetized fish. This has severe implications for animals undergoing procedures. To investigate the effects of tricaine on the central nervous system, we used zebrafish larvae [Tg(elavl3:H2B-GCaMP6s)] at 4 days post fertilization (dpf), expressing a calcium indicator (GCaMP6s) in all neurons, that allows monitoring and quantifying the neuronal activity. After treating larvae with 168 mg/L tricaine, a rapid loss of neuronal activity in the forebrain was observed in confocal microscopy. In contrast, only mild effects were seen in the midbrain and hindbrain. In conclusion, the different larval brain areas showed differences in the sensitivity to tricaine treatment. The effects on the central nervous system are indicative of tricaine's anesthetic function and are consistent with behavioral observations of inactivity and unresponsiveness to touch.

Evaluation of the Effectiveness of Eugenol and MS-222 as Anesthetics in Zebrafish in Repeated Exposures and Post-Anesthesia Behaviour

The increasing use of the zebrafish (Danio rerio) in scientific experiments has made it necessary to implement anesthesia protocols guaranteeing minimum pain and suffering for these animals and ensuring the reliability of the results obtained from their research. Therefore, we aimed to compare the effectiveness of two anesthetics, eugenol and MS-222, in consecutive administrations and evaluate the zebrafish behaviour after repeated anesthesia. Thus, several zebrafish were anaesthetized with eugenol, MS-222, and buffered MS-222 three times repeatedly with a 24-h interval between each exposure. The induction and recovery periods were also timed. Their swimming frequency was determined after each exposure to assess their behaviour after the anesthesia. Anesthesia induction was quicker with eugenol compared to MS-222. However, eugenol presented longer recovery times, which were prolonged after each exposure. Also, the swimming frequency was reduced after each anesthesia with eugenol. The buffered version of MS-222 was more efficacious than the non-buffered one. Both versions of MS-222 did not affect the swimming frequency. Based on these findings, we recommend the utilization of MS-222 buffered rather than eugenol when repeated, brief-duration anesthesia is necessitated for a study.

Eugenol as anesthetic for Cnesterodon decemmaculatus (Cyprinodontiformes, Poeciliidae)

Anesthetics are commonly used in fish for surgery and to facilitate capture, handling and transport in aquaculture and experimental procedures. In research, the selection of the anesthetic depends on its properties and on the recovery time. Eugenol has been pointed out as an effective anesthetic for fish, alternative to traditional drugs. Although Cnesterodon decemmaculatus is widely used as a model in ecological bioassays, no anesthetic protocol has been reported for this species. The aim of the present study was to evaluate the induction time (i.e. time to reach anesthetic stage VI) and recovery time in individuals of C. decemmaculatus subjected to eugenol at a fixed concentration, according to sex and pregnancy status. Forty-one fish were divided into three groups: males, pregnant females and non-pregnant females. They were measured for total length, standard length and weight, and the condition factor (K) was calculated. No significant differences in induction and recovery times were found for sex, pregnancy status and K between groups. Results are a contribution toward the development protocol of a standard anesthetic protocol for C. decemmaculatus.

Treatment of Pain in Fish

This chapter provides an overview of our current understanding of clinical analgesic use in fish. Recently, the efficacy and pharmacokinetics of several analgesic drugs for use in fish have been investigated, and the most important data indicates that μ-opioid agonist drugs (e.g, morphine) are consistently effective as analgesics across fish species. In addition, bath application of some analgesic drugs may be useful, which affords multiple methods for delivering analgesics to fish. Although few published studies of non-steroidal anti-inflammatory drugs administered to fish show promise, we have much to learn about the analgesic efficacy of most drugs in this class.

Embryonic exposure to fentanyl induces behavioral changes and neurotoxicity in zebrafish larvae

The use of fentanyl during pregnancy, whether by prescription or illicit use, may result in high blood levels that pose an early risk to fetal development. However, little is known regarding the neurotoxicity that might arise from excessive fentanyl exposure in growing organisms, particularly drug-related withdrawal symptoms. In this study, zebrafish embryos were exposed to fentanyl solutions (0.1, 1, and 5 mg/L) for 5 days post fertilization (dpf), followed by a 5-day recovery period, and then the larvae were evaluated for photomotor response, anxiety behavior, shoaling behavior, aggression, social preference, and sensitization behavior. Fentanyl solutions at 1 and 5 mg/L induced elevated anxiety, decreased social preference and aggressiveness, and behavioral sensitization in zebrafish larvae. The expression of genes revealed that embryonic exposure to fentanyl caused substantial alterations in neural activity (bdnf, c-fos) and neuronal development and plasticity (npas4a, egr1, btg2, ier2a, vgf). These results suggest that fentanyl exposure during embryonic development is neurotoxic, highlighting the importance of zebrafish as an aquatic species in research on the neurobehavioral effects of opioids in vertebrates.

Behavioural Aversion and Cortisol Level Assessment When Adult Zebrafish Are Exposed to Different Anaesthetics

The use of zebrafish (Danio rerio) as an animal model is growing and occurs in a wide range of scientific areas. Therefore, researchers need better and more appropriate anaesthetics for stressful and/or painful procedures to prevent unpleasant experiences. Thus, we aimed to study if adult zebrafish displayed aversion-associated behaviours (conditioned place aversion) and alterations in cortisol levels when exposed to equipotent concentrations of MS222, propofol/lidocaine, clove oil, or etomidate. Adult AB zebrafish (mixed-sex, N = 177) were randomly assigned to MS222 (150 mg/L), Propofol/Lidocaine (5 mg/L propofol + 150 mg/L lidocaine), Clove Oil (45 mg/L), or Etomidate (2 mg/L) groups. The conditioned place aversion test was used to assess behavioural aversion. Only etomidate resulted in a similar aversion to the positive control group (HCl; pH = 3). Cortisol levels were measured 5 and 15 min after loss of equilibrium. Etomidate induced low levels of cortisol by impairing its synthesis, whereas all the other groups had similar cortisol levels. Based on our data, etomidate was ruled out as an alternative to MS222, as it showed an aversive profile. The remaining protocols were not innocuous, displaying a weak aversive profile when compared to the positive control. In conclusion, a combination of propofol with lidocaine, clove oil, and MS222 were valid candidates for use as anaesthetic protocols.

Screening of Anaesthetics in Adult Zebrafish (Danio rerio) for the Induction of Euthanasia by Overdose

Simple Summary

Although zebrafish are used in vast numbers in laboratories all over the world, no consensus has been reached in the scientific community on a humane, consistent, and effective method for euthanasia of this species. Here, we screened commonly used anaesthetic drugs to see if an overdose could induce loss of reflexes of adult zebrafish in a rapid and reliable manner, and without causing distress. The tested anaesthetics were isoeugenol, clove oil, 2-phenoxyethanol, tricaine, benzocaine, lidocaine hydrochloride, and etomidate. We found that lidocaine hydrochloride, buffered with sodium bicarbonate and ethanol to increase its efficacy, induces loss of reflexes in a fast, predictable, and relatively peaceful manner. We recommend its use for adult zebrafish euthanasia.

Abstract

Zebrafish are often euthanized by overdose of anaesthesia. However, fish may have aversion towards some anaesthetics, and protocol efficacy varies between species. Using wild type adult Danio rerio, we assessed time to loss of opercular beat, righting, and startle reflexes during induction of anaesthetic overdose by either tricaine (0.5 g/L or 1 g/L), benzocaine (1 g/L), 2-phenoxyethanol (3 mL/L), clove oil (0.1%), isoeugenol (540 mg/L), lidocaine hydrochloride (1 g/L), or etomidate (50 mg/L). Initial screening demonstrated that benzocaine and buffered lidocaine hydrochloride achieved the fastest loss of reflexes. The rapid induction times were confirmed when retesting using larger batches of fish. The fastest induction was obtained with 1 g/L lidocaine hydrochloride buffered with 2 g/L NaHCO₃, in which all adult zebrafish lost reflexes in less than 2 min. Next, we monitored signs of distress during benzocaine or buffered lidocaine hydrochloride overdose induction. The results indicated that buffered lidocaine hydrochloride caused significantly less aversive behaviors than benzocaine. Finally, we tested several buffers to refine the lidocaine hydrochloride immersion. The most efficient buffer for euthanasia induction using 1g/L lidocaine hydrochloride was 2 g/L NaHCO₃ with 50 mL/L 96% ethanol, inducing immobility in less than 10 s and with only 2% of adult zebrafish displaying aversive behaviors during treatment.

Development and optimization of an in vivo electrocardiogram recording method and analysis program for adult zebrafish

Clinically pertinent electrocardiogram (ECG) data from model systems, such as zebrafish, are crucial for illuminating factors contributing to human cardiac electrophysiological abnormalities and disease. Current zebrafish ECG collection strategies have not adequately addressed the consistent acquisition of high-quality traces or sources of phenotypic variation that could obscure data interpretation. Thus, we developed a novel platform to ensure high-quality recording of in vivo subdermal adult zebrafish ECGs and zebrafish ECG reading GUI (zERG), a program to acquire measurements from traces that commercial software cannot examine owing to erroneous peak calling. We evaluate normal ECG trait variation, revealing highly reproducible intervals and wave amplitude variation largely driven by recording artifacts, and identify sex and body size as potential confounders to PR, QRS and QT intervals. With this framework, we characterize the effect of the class I anti-arrhythmic drug flecainide acetate on adults, provide support for the impact of a Long QT syndrome model, and establish power calculations for this and other studies. These results highlight our pipeline as a robust approach to evaluate zebrafish models of human cardiac electrophysiological phenotypes.

Adult Zebrafish Anesthesia: A Study of Efficacy and Behavioral Recovery of Different Anesthetics

The use of proper anesthesia in zebrafish research is essential to ensure fish welfare and data reliability. However, anesthesia long-term side effects remain poorly understood. The purpose of this study was to assess anesthesia quality and recovery in adult zebrafish using different anesthetic protocols and to determine possible long-term effects on the fish activity and anxiety-like behaviors after anesthesia. Mixed-sex adult AB zebrafish were randomly assigned to five different groups (Control, 175 mg/L of tricaine methanesulfonate [MS222], 45 mg/L of clove oil, 2 mg/L of etomidate, and 5 mg/L of propofol combined with 150 mg/L of lidocaine) and placed in the respective anesthetic bath. Time to lose the equilibrium, response to touch and to caudal fin pinch stimuli, and recovery after anesthesia administration were evaluated. In addition, after stopping anesthesia, respiratory rate, activity, and anxiety-like behaviors in the novel tank test were studied. Overall, all protocols proved to be adequate for zebrafish anesthesia research as they showed full recovery at 1 h, and only etomidate had minor effects on fish behavior in the novel tank, a validated test for anxiety.

Apex Resection in Zebrafish (Danio rerio) as a Model of Heart Regeneration: A Video-Assisted Guide

Ischemic heart disease is one of the leading causes of deaths worldwide. A major hindrance to resolving this challenge lies in the mammalian hearts inability to regenerate after injury. In contrast, zebrafish retain a regenerative capacity of the heart throughout their lifetimes. Apex resection (AR) is a popular zebrafish model for studying heart regeneration, and entails resecting 10-20% of the heart in the apex region, whereafter the regeneration process is monitored until the heart is fully regenerated within 60 days. Despite this popularity, video tutorials describing this technique in detail are lacking. In this paper we visualize and describe the entire AR procedure including anaesthesia, surgery, and recovery. In addition, we show that the concentration and duration of anaesthesia are important parameters to consider, to balance sufficient levels of sedation and minimizing mortality. Moreover, we provide examples of how zebrafish heart regeneration can be assessed both in 2D (immunohistochemistry of heart sections) and 3D (analyses of whole, tissue cleared hearts using multiphoton imaging). In summary, this paper aims to aid beginners in establishing and conducting the AR model in their laboratory, but also to spur further interest in improving the model and its evaluation.

A suitable anaesthetic protocol for metamorphic zebrafish

Zebrafish are frequently used as a means to investigate development. These studies increasingly require repeated anaesthesia of zebrafish during juvenile (i.e. metamorphic) stages. The effects of anaesthesia during this time remain poorly studied. The aim of this study was to develop a reliable method that can be used for frequently repeated anaesthesia during juvenile stages. Initially, we assessed different concentrations of MS-222, the most commonly used fish anaesthetic, for 30 minute anaesthesia with recovery. We showed that suitable MS-222 doses could be identified for the smallest (7mm) and largest (20mm) fish. However, we found that juvenile fish within a specific metamorphic window (sized between 8-16 mm) were vulnerable to MS-222 and no standard concentration of MS-222 provided reliable anaesthesia under these conditions. Hence we focussed our efforts on identifying a protocol for these stages. We tested six different published anaesthesia protocols P1-P6 where P1, P2 corresponds to 0.01% MS-222, P3, P4: 0.085% 2-phenoxyethanol and P5, P6: 0.00025%/0.0050% Propofol/Lidocaine. In protocols P1, P3, P5 fish were maintained by immersion, whilst in P2, P4 and P6: fish were maintained on an anaesthetic-doused cotton-pad. We assessed reliable anaesthesia using 10 fish for 10 minutes, with full recovery. Our data allowed us to eliminate two of these protocols as unsuitable for short term anaesthesia with recovery of juvenile fish. Extending these studies to explore repeated anaesthesia at 4 day intervals for 20 days under the remaining four protocols, we showed that P1 and P4 were both suitable for repeated anaesthesia, and that P4 was most suitable for imaging. We confirmed that P4 remained suitable when the frequency of anaesthesia was increased to every 2 days. We conclude that this protocol provides a refinement to the current protocol for repeated anaesthesia with recovery of juvenile zebrafish in the vulnerable metamorphic window.

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.

Glutamate Nmda Receptor Antagonists With Relevance To Schizophrenia: A Review Of Zebrafish Behavioral Studies

Schizophrenia pathophysiology is associated with hypofunction of glutamate NMDA receptors (NMDAR) in GABAergic interneurons and dopaminergic hyperactivation in subcortical brain areas. The administration of NMDAR antagonists is used as an animal model that replicates behavioral phenotypes relevant to the positive, negative, and cognitive symptoms of schizophrenia. Such models overwhelmingly rely on rodents, which may lead to species-specific biases and poor translatability. Zebrafish, however, is increasingly used as a model organism to study evolutionarily conserved aspects of behavior. We thus aimed to review and integrate the major findings reported in the zebrafish literature regarding the behavioral effects of NMDAR antagonists with relevance to schizophrenia. We identified 44 research articles that met our inclusion criteria from 590 studies retrieved from MEDLINE (PubMed) and Web of Science databases. Dizocilpine (MK-801) and ketamine were employed in 29 and 10 studies, respectively. The use of other NMDAR antagonists, such as phencyclidine (PCP), APV, memantine, and tiletamine, was described in 6 studies. Frequently reported findings are the social interaction and memory deficits induced by MK-801 and circling behavior induced by ketamine. However, mixed results were described for several locomotor and exploratory parameters in the novel tank and open tank tests. The present review integrates the most relevant results while discussing variation in experimental design and methodological procedures. We conclude that zebrafish is a suitable model organism to study drug-induced behavioral phenotypes relevant to schizophrenia. However, more studies are necessary to further characterize the major differences in behavior as compared to mammals.

Elevated preoptic brain activity in zebrafish glial glycine transporter mutants is linked to lethargy-like behaviors and delayed emergence from anesthesia

Delayed emergence from anesthesia was previously reported in a case study of a child with Glycine Encephalopathy. To investigate the neural basis of this delayed emergence, we developed a zebrafish glial glycine transporter (glyt1 - / -) mutant model. We compared locomotor behaviors; dose-response curves for tricaine, ketamine, and 2,6-diisopropylphenol (propofol); time to emergence from these anesthetics; and time to emergence from propofol after craniotomy in glyt1-/- mutants and their siblings. To identify differentially active brain regions in glyt1-/- mutants, we used pERK immunohistochemistry as a proxy for brain-wide neuronal activity. We show that glyt1-/- mutants initiated normal bouts of movement less frequently indicating lethargy-like behaviors. Despite similar anesthesia dose-response curves, glyt1-/- mutants took over twice as long as their siblings to emerge from ketamine or propofol, mimicking findings from the human case study. Reducing glycine levels rescued timely emergence in glyt1-/- mutants, pointing to a causal role for elevated glycine. Brain-wide pERK staining showed elevated activity in hypnotic brain regions in glyt1-/- mutants under baseline conditions and a delay in sensorimotor integration during emergence from anesthesia. Our study links elevated activity in preoptic brain regions and reduced sensorimotor integration to lethargy-like behaviors and delayed emergence from propofol in glyt1-/- mutants.

A Comparison of Buffered Tricaine Methanesulfonate (MS-222) and Isoeugenol Anesthesia for Caudal Fin Clipping in Zebrafish (Danio rerio)

The purpose of this study was to compare the safety and efficacy of buffered tricaine methanesulfonate (MS-222) and isoeugenol for the anesthesia of zebrafish undergoing caudal fin clipping. Eighty 9 mo Danio rerio (AB strain) zebrafish were allocated to one of 2 equal groups: buffered MS-222 (168 mg/L, n = 40) or isoeugenol (20 mg/L, n = 40). The time to induction of anesthesia was significantly shorter in the isoeugenol group (141 ± 70 s) than in the MS-222 group (207 ± 103 s). The time to recovery from anesthesia was also shorter in the MS-222 group (373 ± 125 s) than in the isoeugenol group (491 ± 176 s). No obvious displays of distress or aversion to anesthesia were observed in either group. No difference was detected in the proportion of zebrafish that became anesthetized with either drug. One male zebrafish in the buffered MS-222 group was found dead at the 1-h post-procedural monitoring time point, but there was no difference between groups in the proportion of fish that survived anesthesia to the end of experiment. In conclusion, the safety and efficacy of buffered MS-222 (168 mg/L) and isoeugenol (20 mg/L) was similar for zebrafish undergoing anesthesia for caudal fin clipping.

Larval zebrafish as an in vitro model for evaluating toxicological effects of mycotoxins

The presence of mycotoxins in food has created concern. Mycotoxin prevalence in our environment has changed in the last few years maybe due to climatic and other environmental changes. Evidence has emerged from in vitro and in vivo models: some mycotoxins have been found to be potentially carcinogenic, embryogenically harmful, teratogenic, and to generate nephrotoxicity. The risk assessment of exposures to mycotoxins at early life stages became mandatory. In this regard, the effects of toxic compounds on zebrafish have been widely studied, and more recently, mycotoxins have been tested with respect to their effects on developmental and teratogenic effects in this model system, which offers several advantages as it is an inexpensive and an accessible vertebrate model to study developmental toxicity. External post-fertilization and quick maturation make it sensitive to environmental effects and facilitate the detection of endpoints such as morphological deformities, time of hatching, and behavioral responses. Therefore, there is a potential for larval zebrafish to provide new insights into the toxicological effects of mycotoxins. We provide an overview of recent mycotoxin toxicological research in zebrafish embryos and larvae, highlighting its usefulness to toxicology and discuss the strengths and limitations of this model system.

A comparison between chemical and gas hypoxia as models of global ischemia in zebrafish (Danio rerio)

BACKGROUND

Zebrafish models for neurovascular diseases offer new methods for elucidation of molecular pathways to tissue damage. External fertilization and high fecundity provide opportunities for transgenics and other forms of genetic manipulation that are more accessible than offered by mammalian models of disease. Furthermore, behavioral analyses of zebrafish allow for connection of molecular pathways to organismal outputs such as locomotion, learning, and memory. Unfortunately, a zebrafish model of hypoxia-ischemia has been slow to catch on, possibly due to hypoxia exposure protocols that are challenging to reproduce and result in high mortality.

METHODS

In this study, we have introduced a predictable and simple method of hypoxia induction, the addition of sodium sulfite to aquarium water. The effects of this treatment on zebrafish locomotion were compared to those of zebrafish exposed to hypoxia induced by nitrogen gas bubbling, a method used in previous reports.

RESULTS

We found that hypoxia induced by sodium sulfite significantly impaired locomotion in the hours following treatment, and its effects did not differ from those caused by nitrogen gas hypoxia.

CONCLUSION

These results indicate that hypoxia by sodium sulfite represents an effective and easily reproducible method for the study of hypoxia-ischemia in zebrafish.

Development of a Simple ImageJ-Based Method for Dynamic Blood Flow Tracking in Zebrafish Embryos and Its Application in Drug Toxicity Evaluation

This study aimed to develop a simple and cost-effective method to measure blood flow in zebrafish by using an image-based approach. Three days post fertilization (dpf) zebrafish embryos were mounted with methylcellulose and subjected to video recording for tracking blood flow under an inverted microscope equipped with a high-speed CCD camera. In addition, Hoffman lens was used to enhance the blood cell contrast. The red blood cell movement was tracked by using the TrackMate plug-in in the ImageJ image processing program. Moreover, Stack Difference and Time Series Analyzer plug-in were used to detect dynamic pixel changes over time to calculate the blood flow rate. In addition to blood flow velocity and heart rate, the effect of drug treatments on other cardiovascular function parameters, such as stroke volume and cardiac output remains to be explored. Therefore, by using this method, the potential side effects on the cardiovascular performance of ethyl 3-aminobenzoate methanesulfonate (MS222) and 3-isobutyl-1-methylxanthine (IBMX) were evaluated. MS222 is a common anesthetic, while IBMX is a naturally occurring methylxanthine. Compared to normal embryos, MS222- and IBMX-treated embryos had a reduced blood flow velocity by approximately 72% and 58%, respectively. This study showed that MS222 significantly decreased the heart rate, whereas IBMX increased the heart rate. Moreover, it also demonstrated that MS222 treatment reduced 50% of the stroke volume and cardiac output. While IBMX decreased the stroke volume only. The results are in line with previous studies that used expensive instruments and complicated software analysis to assess cardiovascular function. In conclusion, a simple and low-cost method can be used to study blood flow in zebrafish embryos for compound screening. Furthermore, it could provide a precise measurement of clinically relevant cardiac functions, specifically heart rate, stroke volume, and cardiac output.

Review on the use of zebrafish embryos to study the effects of anesthetics during early development

Over the years, the potential toxicity of anesthetics has raised serious concerns about its safe use during pregnancy. As evidence emerged from research in animal models, showing that some anesthetic drugs are potential teratogenic, the determination of the risk of exposures to anesthetic drugs at early life stages became mandatory. However, due to inaccessibility and ethical constrains related to experimental conditions, the use of early life stages in mammalian models is limited. In this regard, some animal and nonanimal models have been suggested to surpass mammalian use in experimentation. Among them, the zebrafish embryo test has been recognized as a promising alternative in toxicology research, as well as an inexpensive and practical test. Substantial information collected from developmental research following compounds exposure, has contributed to the application of zebrafish assays in research, although only a few studies have focused on the use of early life stages of zebrafish to evaluate the developmental effects of anesthetics. Based on the recent advances of science and technology, there is a clear potential for zebrafish early life stages to provide new insights into anesthetics teratogenicity. This review provides an overview of recent anesthesia research using zebrafish embryos, demonstrating its usefulness to the anesthesia field, discussing the recent findings on various aspects related to the effects of anesthetics during early life development and the strengths and limitations of this model system.

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.

Anesthetic protocol for microinjection-related handling of Siberian sturgeon (Acipenser baerii; Acipenseriformes) prolarvae

An anesthetic protocol was optimized for microinjection-related handling of Siberian sturgeon (Acipenser baerii; Acipenseriformes) prolarvae, an extant primitive fish species commonly grown in aquaculture. Comparative examinations of three selected anesthetics (clove oil, lidocaine, and MS-222) with a dosage regime of 50, 100, 200, and 400 mg/L indicated that MS-222 was the most efficient agent for Siberian sturgeon prolarvae, as evidenced by the fast induction of anesthesia with quick and uniform recovery. Meanwhile, clove oil should be avoided, due to prolonged recovery times varying widely between individuals. None of the tested anesthetics significantly affected prolarval viability at any of the dosage regimes tested in this study. Based on an analysis of the duration of an unconscious state in air, we recommend a dose of 200 mg/L MS-222 for microinjection. Recovery time after use of this dose was influenced by the prolarval age and the development of gills, in which prolarvae older than 3 days after hatching required longer recovery times than did younger prolarvae. Post-recovery behavioral assessment showed no apparent difference between MS-222-anesthetized and non-anesthetized prolarvae in their swimming behavior and phototactic responses. Applicability of currently developed anesthetic protocol using MS-222 in larval microinjection was demonstrated with the injection of a visible dye to the anesthetized prolarvae, followed by the analysis of post-recovery viability. Taken together, the present anesthetic protocol based on 200 mg/L of MS-222 could provide researchers with practical usefulness with good safety margins for the micromanipulation and other related handlings of Siberian sturgeon prolarvae.