An Investigation into the Mechanism Mediating Counterillumination in Myctophid Fishes (Myctophidae).

AbstractCounterillumination is a camouflage strategy employed primarily by mesopelagic fishes, sharks, crustaceans, and squid, which use ventral bioluminescence to obscure their silhouettes when viewed from below. Although certain counterilluminating species have been shown to control the intensity of their ventral emissions to match the background downwelling light, the feedback mechanism mediating this ability is poorly understood. One proposed mechanism involves the presence and use of eye-facing photophores that would allow simultaneous detection and comparison of photophore emissions and downwelling solar light. Eye-facing photophores have been found in at least 34 species of counterilluminating stomiiform fishes and the myctophid