Three-dimensional motion tracking reveals a diving component to visual and auditory escape swims in zebrafish larvae

Escape behaviors have been studied in zebrafish by neuroscientists seeking cellular-level descriptions of neural circuits but few studies have examined vertical swimming during escapes. We analyzed three-dimensional swimming paths of zebrafish larvae during visually-evoked and auditory-evoked escapes while the fish were in a cubical tank with equal vertical and lateral range. Visually evoked escapes, elicited by sudden dimming of ambient light, consistently elicited downward spiral swimming (dives) with faster vertical than lateral movement. Auditory taps also elicited rapid escape swimming with equivalent total distance traveled but with significantly less vertical and more lateral movement. Visually evoked dives usually ended with the zebrafish hitting the bottom of the 10 cm³ tank. Therefore, visually evoked dives were also analyzed in a tubular tank with 50 cm of vertical range, and in most cases larvae reached the bottom of that tank during a 120 s dimming stimulus. Light-evoked spiral diving in zebrafish may be an innate defense reflex against specific predation threats. Since visual and auditory escapes are initially similar but dives persist only during visual escapes, our findings lay the groundwork for studying a type of decision-making within zebrafish sensorimotor circuits.