The Luminescent Systems of Pony Fishes

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Abstract
The anatomy of bioluminescent organs and mode of light production in 18 species of pony fish have been investigated using fresh and preserved material. The luminescent systems are similarly arranged in all. Basically, the system consists of a light organ located at the distal end of the esophagus, and a series of abdominal accessory structures positioned in tandem for controlling light intensity and for directing and dispersing the light. Light is produced by numerous symbiotic luminous bacteria in the light organ. A simple classification of the luminescent systems is proposed.The light organs ofLeiognathus elongatusandL. rivulatusshow marked sexual dimorphism. The bacteria present in the light organs of many pony fishes are easily culturable, but not those fromL. elongatus. Electron micrographs of the light organs ofL. elongatusandL. rivulatusshow the presence of numerous rod‐shaped bacteria measuring approximately 0.8 µ x 2.4 µ and 0.8 µ x 7.3 µ, respectively. It is concluded that the light organ ofL. elongatuscontains another example of a type of non‐culturable luminous bacteria that have been found elsewhere. Such bacteria appear to require from the host some special factor for growth and luminescence.