The research team, led by investigators at MacEwan University and the University of Alberta in Canada, set out to address a practical bottleneck in addiction neuroscience. Traditional zebrafish ethanol exposure paradigms typically involve repeated daily doses or continuous immersion for one to three weeks before withdrawal is assessed. Such long schedules are costly in animal numbers, facility time, and experimental complexity. The condensed paradigm developed in the new study involved three one-hour exposures to 0.8 percent ethanol per day over just five consecutive days, administered at 09:00, 12:00, and 15:00. This schedule was designed to more closely mirror the intermittent, binge-like drinking patterns seen in humans at risk for Alcohol Use Disorder, where cycles of intoxication and relative abstinence drive the stress-craving cycle central to the disorder.

Zebrafish have become a cornerstone of neuropharmacological research for good reason. They breed prolifically, are inexpensive to maintain, possess a fully sequenced genome with approximately 70 percent protein-coding gene homology to humans, and readily absorb water-soluble chemicals directly from their tank water. This last feature makes dosing remarkably consistent: fish are simply transferred into tanks containing the desired ethanol concentration for a fixed period, then rinsed and returned to their home tanks. In the new study, 144 adult AB/wildtype zebrafish aged six to seven months were used, housed in Techniplast ZebTEC multilinking systems with carefully controlled water quality, temperature, and light cycles. All procedures were approved by the MacEwan University Animal Research Ethics Board under Canadian Council for Animal Care guidelines, and no mortality occurred over the course of the experiment.

The experiment used a 2 × 3 × 2 factorial design with three independent variables: ethanol treatment versus habitat water control, withdrawal duration of 2, 4, or 8 days, and sex. Fish were dosed in groups of 12 in 3-liter tanks, with two replicate tanks per condition across two identical experimental sets conducted one month apart. Following the final dose, fish were assigned to withdrawal periods before behavioral testing. The researchers used the open field test, a well-validated assay for anxiety-like behavior in zebrafish, consisting of a white plastic cylinder 26.3 centimeters in diameter with 5 centimeters of habitat water. Fish were individually netted and placed in the arena with no more than 2 seconds of transfer time, and 10-minute trials were recorded using EthoVision XT motion tracking software.

The open field test divides the arena into three concentric zones: a center zone (0–7.9 centimeters in diameter), a transition zone (7.8–16.3 centimeters), and a thigmotaxis zone near the wall (16.4–26.3 centimeters). Thigmotaxis, the tendency to stay close to walls, is a robust metric of anxiety-like behavior in zebrafish, analogous to wall-hugging in rodents. The software also quantified distance travelled, mean absolute angular velocity, time spent highly mobile (defined using frame-to-frame changes in fish pixels with a threshold of 60 percent), and time spent immobile (threshold of 5 percent). Statistical significance was set at α = 0.05, and mixed-effects analyses with Holm-Šídák post hoc tests were used to examine the effects of treatment, withdrawal duration, and sex on all behavioral variables.

The results revealed a complex behavioral profile. Regardless of withdrawal duration, ethanol-treated fish showed significant increases in immobility and mean absolute angular velocity compared to controls, indicating that the condensed paradigm produced measurable locomotor changes that persisted across the withdrawal period. However, the most striking effects emerged only at 8 days of withdrawal. At this time point, ethanol-treated fish spent significantly less time highly mobile than controls, and their spatial preferences shifted dramatically: they spent significantly more time in the transition zone and significantly less time in the thigmotaxis zone compared to control fish. Notably, no significant differences were found in overall distance moved, center zone preference, or between male and female fish at any withdrawal duration.

The direction of the spatial preference change surprised the researchers. Increased thigmotaxis preference is typically interpreted as an anxiogenic response, consistent with the anxiety-like withdrawal phenotype seen in many previous zebrafish studies. The opposite pattern observed here—reduced wall preference and increased transition zone occupancy—suggests that the condensed dosing paradigm may not produce a traditional anxiogenic withdrawal response. The authors propose several explanations: the observed preference could reflect a disinhibited behavioral state resulting from withdrawal effects, or the overriding locomotor alterations may be stronger than anxiogenic location preferences. In other words, the anxiogenic locomotor patterns may be independent of the fish’s location preference, with fish freezing outside the thigmotaxis zone rather than inside it.

From a neurochemical perspective, ethanol positively modulates GABAergic signaling as a GABA(A) receptor agonist, producing biphasic effects that depend on concentration and duration. Low to intermediate concentrations dampen excitatory transmission and produce anxiolytic-like effects, whereas higher concentrations produce depressant-like effects. Chronic exposure induces neuroadaptations across multiple neurotransmitter systems, leading to anxiogenic-like symptoms upon withdrawal due to dysregulation of the hypothalamic-pituitary-interrenal axis and increased excitatory GABAergic transmission. Repeated ethanol exposure also contributes to oxidative stress, which damages mitochondrial complexes and the central nervous system and may require time to normalize following cessation, potentially explaining the delayed behavioral withdrawal symptoms observed at 8 days.

The delayed emergence of the withdrawal phenotype at 8 days is consistent with previous research showing that repeated alcohol exposure produces lasting behavioral and neurobiological adaptations that evolve over the course of withdrawal and depend on ethanol dose and duration. Previous studies have reported delayed withdrawal effects with intermittent dosing schedules, where significant differences in behavioral tests were not detected until the 6th or 7th day of withdrawal. The new findings support the idea that ethanol withdrawal phenotypes become more pronounced from 2 days onward, with the specific direction and magnitude of effects varying with dose, exposure duration, and withdrawal period.

The lack of sex differences in the present study may be due to the condensed nature of the dosing paradigm, insufficient sample sizes within each subgroup, or the genetic strain of the fish. Previous research has reported mixed findings on sex-specific responses to ethanol in zebrafish, with some studies showing males more sensitive to acute exposure and others showing females more active during withdrawal. The authors acknowledge several limitations, including the reliance solely on behavioral measures without assessment of neurochemical systems like glutamate, GABA, serotonin, or dopamine, nor changes in the hypothalamic-pituitary-interrenal axis, brain alcohol levels, or stress hormones such as cortisol. Future studies should vary ethanol concentration, exposure duration, number of doses per day, and withdrawal intervals to optimize the condensed paradigm.

The overall goal of the study was to develop a condensed repeated daily dosing paradigm that more accurately represents the stress-craving cycle seen in frequent drinkers at risk for Alcohol Use Disorder. The significant increases in immobility and mean absolute angular velocity, along with decreased high mobility at 8 days of withdrawal, indicate a response phenotype worthy of further analysis. The condensed model is more efficient for high-throughput studies and may be useful for evaluating pharmacological treatments and other pharmacological agents relevant to AUD withdrawal management. As existing pharmacological treatments for AUD continue to suffer from undesirable side effects and long treatment durations, this efficient new paradigm offers a practical tool for accelerating the development and testing of new therapeutic approaches.

Subject of Research: Behavioral impact of condensed repeated ethanol dosing on withdrawal in adult zebrafish (Danio rerio)

Article Title: Behavioral impact of condensed repeated ethanol dosing on withdrawal in adult zebrafish (Danio rerio)

Article References: Prince, R., Steman, T., Hagen, E. V., Johnson, A. L., Zhang, Y., & Hamilton, T. J. (2026). Behavioral impact of condensed repeated ethanol dosing on withdrawal in adult zebrafish (Danio rerio). Frontiers in Systems Neuroscience, 20, Article 1924496. https://doi.org/10.3389/fnsys.2026.1924496

Image Credits: AI Generated

DOI: 10.3389/fnsys.2026.1924496

Keywords: Behavioral, impact, condensed, repeated, ethanol, dosing, withdrawal, adult, zebrafish, Danio, rerio, scientific research