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Defensive Behavior
Rheotaxis
The automatic orientation of a fish to face into a current - essential for holding position in rivers and streams.
Trigger: Environment Function: Prevents downstream displacement and orients fish for feeding Observable in aquarium
📖 Overview
Drop a trout into a river and it will instantly turn to face upstream. This is rheotaxis - a reflexive orientation to current that lets stream fish hold their position and monitor for drifting food. Detected primarily via the lateral line, rheotaxis works even in complete darkness or in blind cave fish.
👁️ How to Observe
In aquariums with strong powerheads, watch fish align themselves. Even goldfish will orient into a simulated current.
✨ Fun Fact
Blind cave fish, which have no eyes, still orient upstream flawlessly - proof that rheotaxis is fundamentally a lateral line sense, not a visual one.