Alex Davis and Sonke Johnson on the Hatchetfish

Hatchetfish with photophores marked

Biograd Alex Davis and Sonke Johnson et al. have published “Evidence That Eye-Facing Photophores Serve as a Reference for Counterillumination in an Order of Deep-Sea Fishes” in Proceedings of the Royal Society B, June 2, 2020.  The paper examines three families of fish who live at intermediate depths with some light from the surface, and whose bodies therefore cast a shadow downward.  In order to make the shadow disappear, they must match the light output from photophores on their bellies to the local ambience.  They do this with an outward-shielded photophore that transmits information on the surrounding light level to the retina.  This had already been proposed for one species, but now Davis et al. have shown that numerous species with ventral illumination have an eye-facing photophore, while two species without counterillumination also lack this special organ.  Well done!

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Lights in the Eyes for Better Disguise