Luminous organ found in fish.

the organ in which bioluminescent light is produced

an organ that produces light, usually on belly or head, as in lanternfishes

A glowing organ that contains light-producing chemicals.

Light emitting (bioluminescent) organ.

Photophores are light-producing organs that are found in some fish, cephalopods, and crustaceans. Sharks like the lanternsharks have luminescent photophores; these sharks live in the deep seas in a dark environment.

A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fishes and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors http://tolweb.org/accessory/Cephalopod_Photophore_Terminology?acc_id=2015. The light can be produced from compounds during the digestion of prey, from specialized mitochondrial cells in the organism, called photocytes ("light producing" cells) from the nomenclature of ichthyology, or, similarly, associated with symbiotic bacteria in the organism that is cultured.