Physical Description

  • Long, slender fish with long, continuous dorsal (top) and pelvic (bottom) fins.
  • Olive brown to bronze to dark iridescent purple coloration on back, paler coloring on sides, yellow on belly.
  • White space under eyes with a black crescent below.
  • Hundreds of photophores (light-emitting organs) line the underside of their head and body to attract prey.
  • Can be up to 15 inches long.


  • Sitka, Alaska to Magdalena Bay, southern Baja California, Mexico.
  • Two populations: one Oregon northward and one San Francisco southward.


  • Live from the intertidal (area of shoreline covered at high tide and uncovered at low tide) to the deep sea.
  • Live over sandy and muddy bottoms.
  • Males make nests under large rocks or seaweed in intertidal zone, and are sometimes fully out of the water.


  • Adults are often in deep water but travel to the shallow intertidal in spring and summer to breed.
  • Males produce a loud droning hum to attract females to their nesting site under large rocks and seaweed.
  • Females will lay her orange eggs in the nesting site and then leave.
  • The males will fertilize the eggs and tend to the nest.
  • The eggs will hatch in approximately four weeks into miniature versions of the adults.
  • In another 4-6 weeks, the juveniles will leave the nest and swim into the deep ocean.


  • Crustaceans and other fishes.


  • Seals and sea lions.

Interesting Facts

  • For years, residents of houseboats in Sausalito, California complained of a noise on summer nights that was so loud that they often couldn’t sleep. The droning hum sounded like it was manmade, like a group of motorboats or large submarines, but it was actually the vocalizing hum of male plainfin midshipman! They make the noise by contracting the drumming muscles on their swim bladder. 
  • Plainfin midshipman can make other noises. They can not only hum, but can also grunt and growl.
  • When adults are out of the water, they can breathe air!

Hear a Midshipman

Sources: Discovery of Sound in the Ocean; FishBase; American Fisheries Society; Elkhorn Slough National Estuarine Research Reserve

Photo: Herb Gruenhagen