Zebrafish Mirror Biting (Aggression)
Overview
The zebrafish mirror biting test quantifies aggressive behavior by presenting a mirror on one wall of the test tank, eliciting the full repertoire of agonistic displays directed at the perceived intruder (the fish own reflection). Male zebrafish respond to their mirror image with approach, lateral displays (broadside posturing with erect fins), frontal displays, and direct biting attempts at the mirror surface, providing a standardized measure of aggression that avoids injury to a real opponent. The aggressive circuitry in zebrafish involves serotonergic neurons in the dorsal raphe, dopaminergic input from the posterior tuberculum, and hypothalamic neuropeptide systems including arginine vasotocin (AVT, the teleost vasopressin homologue), with the lateral habenula acting as a key modulator of aggressive motivation.
The primary dependent variables include the number of mirror bites (direct contact or near-contact with the mirror surface), total time spent in the mirror-proximal zone (typically defined as within 2 cm of the mirror), frequency and duration of lateral displays, and approach latency to the mirror after initial placement. The mirror interaction index, calculated as mirror-zone time divided by total session time, provides a normalized aggression score. Bout analysis segments aggressive episodes to measure attack bout frequency, mean bout duration, and inter-bout intervals, revealing temporal dynamics of aggressive arousal and fatigue across the session.
ConductMaze detects mirror-directed behaviors using a combination of position tracking (proximity to the mirror wall) and body-orientation analysis, automatically scoring approach events, mirror-zone occupancy, and display postures. The system distinguishes between passive mirror proximity and active aggressive engagement by analyzing velocity and orientation angle relative to the mirror surface. Per-minute temporal profiles reveal escalation patterns and aggressive fatigue, while batch processing supports parallel aggression screening across multiple tanks.
Trial Flow
Tank Preparation
Fill test tank with system water (26-28 C); position mirror flush against one end wall
Fish Introduction
Transfer individual fish to the tank with mirror concealed; acclimate for 5 min
Mirror Reveal
Remove opaque cover to expose mirror; start behavioral recording
Behavioral Recording
Record aggressive interactions for 5 minutes with side-view camera at 30 fps
Bite Detection
Score mirror bites when fish nose contacts or approaches within 2 mm of mirror surface at high velocity
Display Classification
Classify lateral displays (broadside, erect fins) and frontal displays based on body orientation
Metric Computation
Calculate bite count, mirror zone time, display frequency, approach latency, and interaction index
Trial End
Cover mirror; return fish to home tank; clean tank between subjects
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Test Duration | duration | 300 | Duration of mirror exposure recording in seconds (standard 5 min) |
| Water Temperature | temperature | 27.0 | System water temperature in degrees Celsius (26-28 C optimal) |
| Tank Length | distance | 24.0 | Internal tank length in centimeters |
| Tank Width | distance | 8.0 | Internal tank width in centimeters |
| Water Depth | distance | 15.0 | Water depth in centimeters |
| Mirror Zone Width | distance | 2.0 | Width of the mirror-proximal interaction zone in centimeters |
| Acclimation Period | seconds | 300 | Pre-mirror acclimation time with mirror concealed in seconds |
| Time Bin Size | seconds | 60 | Duration of each time bin for temporal aggression analysis in seconds |
| Sex | enum | male | Subject sex: male (typically more aggressive) or female |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Mirror Bites | count | Number of direct bite attempts at the mirror surface |
| Mirror Zone Time | seconds | Total time spent within the mirror-proximal interaction zone |
| Mirror Interaction Index | ratio | Mirror zone time / total session time (0-1 scale) |
| Lateral Displays | count | Number of broadside postures with erect fins directed at the mirror |
| Approach Latency | seconds | Time from mirror reveal to first entry into the mirror zone |
| Mean Bout Duration | seconds | Average duration of continuous aggressive interaction bouts |
| Total Distance | cm | Cumulative distance swum during the test session |
Sample Data
| Subject | Treatment | Mirror Bites | Mirror Zone Time (s) | Interaction Index | Lateral Displays | Approach Latency (s) |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Serotonergic pharmacology — evaluating how SSRIs, 5-HT1A agonists, and tryptophan manipulation alter aggressive motivation and display frequency
- 2Neuropeptide aggression research — characterizing the roles of arginine vasotocin, isotocin, and hypothalamic peptides in zebrafish agonistic behavior
- 3Sex difference analysis — quantifying sexually dimorphic aggression patterns and their hormonal regulation by androgens and estrogens
- 4Strain aggression profiling — establishing baseline aggression levels across commonly used laboratory strains (AB, TU, WIK, Casper)
- 5Social hierarchy neuroscience — combining mirror aggression scores with group-housed dominance rankings to predict social status
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