Tubed Siphonfish

Siphamia tubifer, commonly referred to as the sea urchin cardinalfish, is a small coral reef fish, approximately 7 cm in length, belonging to the family Apogonidae. Its geographical distribution spans from East Africa to the 🇵🇫 French Polynesian Islands. This species inhabits depths ranging from 1 to 100 meters, although it is predominantly found between 1 and 18 meters.

During daylight hours, the sea urchin cardinalfish seeks refuge among the spines of sea urchins and becomes active at night for feeding purposes. A notable reproductive behavior in male Siphamia tubifer is mouthbrooding; they carry fertilized eggs in their mouths until the larvae reach the preflexion stage, at which point they are released.

This species engages in a facultative symbiotic relationship with the bacterium Photobacterium mandapamensis, which facilitates bioluminescence via a specialized light organ situated in the fish's abdomen. The acquisition of this bacterium is believed to occur through the ingestion of seawater once the light organ is predominantly developed. The bioluminescence mechanism comprises primarily of a ventral light organ that houses the bacteria and an adjustable shutter lens within the abdomen, which the fish can manipulate to regulate emitted light.

Research indicates that, at twilight, Siphamia tubifer emerges from its sea urchin habitat, utilizing bioluminescence to attract and consume zooplankton in proximity to the ocean floor. Upon nightfall, the fish ceases luminescence and retreats to the safety of its sea urchin companion.