Larval zebrafish H2B bulk spectral sensitivity

The encoding of light increments and decrements by separate On- and Off-
systems is a fundamental ingredient of vision, which supports edge
detection and makes efficient use of the limited dynamic range of visual
neurons. Theory predicts that the neural representation of On- and
Off-signals should be balanced, including across an animals’ visible
spectrum. Here we find that larval zebrafish violate this textbook
expectation: in the zebrafish brain, UV-stimulation near exclusively gives
On-responses, blue/green stimulation mostly Off-responses, and red-light
alone elicits approximately balanced On- and Off-responses. We link these
findings to zebrafish visual ecology, and suggest that the observed
spectral tuning boosts the encoding of object “colourfulness”, which
correlates with object proximity in their underwater world.