Abstract
THE characteristic ventral distribution of fish photophores suggests that their luminescence reduces the silhouette when viewed against a background of downwelling light1–3. This hypothesis is supported by demonstration of direct neural control of photophores in several species of myctophids and by morphological and behavioural indications that Tarletonbenia crenularis matches its luminescence to background illumination by visually monitoring a supraorbital photophore4,5. There is similar evidence for other taxa: shallow water leiognathids emit light in response to brief photic stimulation and mid-water squid have photosensitive vesicles which may participate in countershading6–8. Here we report photometric measurements of myctophid bioluminescent responses to light levels comparable with those occurring in their environment.
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