Pachystomias is one of three deep-sea fish that can produce red light bioluminescence, along with Aristostomias, Chirostomias, and Malacosteus.

In addition to producing blue light via postorbital photophores, Pachystomias also possess suborbital and preorbital cephalic photophores that are capable of producing far-red bioluminescence, with wavelength emissions of over 650 nm.

[2] The suborbital and preorbital organs have been observed to produce both bright flashes as well as steady glows.

[3] However, deep-sea loose-jawed dragonfish, including Pachystomias, are sensitive to long-wave light and are able to detect their own bioluminescence.

Because the ability to detect red light is rare, it is thought that this adaptation could serve deep-sea loose-jawed dragonfish by acting as a prey-detection system, as well as for intraspecific communication.