Phosichthyidae

Phosichthyidae is a family of small, deep-sea ray-finned fish commonly known as lightfishes or luminous fishes. They are related to the Gonostomatidae (bristlemouths) and Sternoptychidae (hatchetfishes) and share the order Stomiiformes. Phosichthyids are characterized by their photophores, light-producing organs, located along their ventral surface. These photophores are used for counterillumination, camouflage against predators in the dimly lit mesopelagic zone, and possibly for communication.

These fish are typically found in tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. They occupy depths ranging from the epipelagic zone down to the bathypelagic zone, with the highest concentrations often found between 200 and 1000 meters.

Phosichthyids are relatively small, generally not exceeding 10 centimeters in length. They possess slender bodies, large eyes, and small mouths. Their diet consists primarily of plankton and small crustaceans. They are an important component of the deep-sea food web, serving as prey for larger predatory fish and marine mammals.

The classification of genera within the Phosichthyidae family has undergone revisions. Genera generally accepted include Ichthyococcus, Phosichthys, Pollichthys, Polymetme, and Vinciguerria. These genera are distinguished by slight variations in morphology, photophore arrangements, and fin ray counts.

Because of their deep-sea habitat and small size, Phosichthyids are not commercially fished. They are primarily of scientific interest, particularly in studies of deep-sea ecology, bioluminescence, and evolutionary relationships among stomiiform fishes.