Pacific Portholefish, Diplophos taenia
Pacific Portholefish, Diplophos taenia. Fish caught from coastal waters off Point Palmilla, Baja California Sur, February 2014. Regurgitated by a Highfin Sand Perch, Diplectrum labarum. Length: 8.5 cm (3.3 inches). Identification courtesy of Cindy Klepadio, Scripps Institution of Oceanography, La Jolla, California.
The Pacific Portholefish, Diplophos taenia, is a member of the Bristlemouth or Gonostomatidae Family. This fish is uncommon and seldom seen by humans and has not been given a Spanish name. It received its common name from first be observed out of a porthole in a ship. Globally, there are five species in the genus Diplophos, of which one, this species, is found in Mexican waters of both the Atlantic and the Pacific Oceans.
The Pacific Portholefish has a very slender elongated body that tapers significantly from head to tail. They are uniformly dull grayish brown in color and transition to silver ventrally. Their fins are transparent. Their head is large with a pointed snout, mid-sized eyes, and a large mouth that extends to the rear margin of the eyes. Their anal fin has no spines and 59 to 72 rays; their caudal fin is small and forked; and their dorsal fin has 10 or 11 rays and no spines. They have 2 conspicuous rows of photophores (light producing organs) that run ventrally from their head to the base of their tail. Reproduction is oviparous with planktonic eggs and larvae.
The Pacific Portholefish is a bathypelagic species found over sandy bottoms. They reach a maximum of 28 cm (11 inches) in length. They are vertical migrators that move toward the surface during the night to feed on plankton and return to depths of at least 750 m (2,500 feet) during the day to avoid predation. The Pacific Portholefish is rare and is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Pacific Portholefish is a global species found in all tropical and subtropical seas from 40oN latitude to 30oS latitude. It is a resident of all Mexican waters of the Atlantic and the Pacific Oceans.
The Pacific Portholefish is difficult to identify. A correct identification requires a professional ichthyologist that specializes in Stomiiformes, the deep water dragonfish, hatchetfish, lightfish, loosejaws, and viperfish. I am fortunate to have had productive discussions with Cindy Klepadio, Scripps Institution of Oceanography, La Jolla, California about this fish which has been added to the SIO Fish Collection.
From a conservation perspective the Pacific Portholefish is currently considered to be of Least Concern with stable widely distributed populations. They are relatively small, exceedingly rare, and of limited interest to most.