Enhanced retinal longwave sensitivity using a chlorophyll-derived photosensitiser in Malacosteus niger, a deep-sea dragon fish with far red bioluminescence.

Through partial bleaching of both visual pigment extracts and cell suspensions we show that the deep-sea stomiid Malacosteus niger, which produces far red bioluminescence, has two visual pigments within its retina which form a rhodopsin/porphyropsin pigment pair with lambda max values around 520 and 540 nm, but lacks the very longwave sensitive visual pigments (lambda max > 550 nm) observed in two other red light producing stomiids. The presence of only a single opsin gene in the M. niger genome was confirmed by molecular and cladistic analysis. To compensate for its apparently reduced longwave sensitivity compared to related species, the outer segments of M. niger contain additional pigments, which we identify as a mixture of defarnesylated and demetallated derivatives of bacteriochlorophylls c and d, that are used as a photosensitiser to enhance its sensitivity to longwave radiation.