[3] There it inhabits shallow waters and will make migrations every spring to the rocky intertidal zones of the coast to breed.

[4] The ”midshipman” name comes from the line of photophores found on their body; they are positioned similarly to the uniforms of midshipmen—the lowest ranking naval officer of any navy.

It is brownish to olive to iridescent purple dorsally, becoming lighter on the sides and yellowish/golden on the belly, though this can depend on sex.

[7] Similar species include: During the nonbreeding season, the plainfin midshipmen typically inhabit moderately deep ocean waters off the coast of Pacific coast of North America, from Canada to Baja California.

They can range from shallow water just below the tide to depths of 366 m and prefer sandy and muddy bottoms.

[8] During the late spring and early summer, they migrate from the depths to the intertidal zones of the coast to breed.

[11] The Type I male claims a nest site, which is generally under a rocks or boulders in the intertidal zone.

[13] The male tends them by fanning them, keeping the nest clean, and hydrating them if they begin to desiccate at low tide.

He protects the larvae post-hatching until they reach their juvenile stage and leave the nest, about 45 days after fertilization.

[11] Type II males at times display behavior of fanning their own sperm into a nest containing a gravid female.

[11] Type II males can be mistaken as gravid females as their abdomen distend due to enlarged testes.

After hatching, the embryos remain attached to the cavity wall by the yolk sacs for about a month, after which they will detach and bury in the mud.

This crustacean has a similar, but not identical, luciferin compound which can apparently function in the photophores of the fish, as well.

It is thought that the fish obtains its luciferin in the wild by eating this type of crustacean, perhaps a relative such as Vargula tsujii, and that the nonluminescent northern population does not have any of these available to them.

He utters long strings of shorter grunts and growls while fighting, but his courtship call is more of a prolonged hum.

During the breeding season, hormones induce the microscopic anatomy of the female's saccules to change in such a way that she can better sense the harmonics of the male's calls.

Where there are many breeding males, the sound of many simultaneous long, loud underwater courtship calls can be clearly heard on land.

[28] Its calling is most intense between midnight and 6:00 a.m.[29] Despite its annoying behavior the fish inspired an affectionate local tribute in Sausalito, the Humming Toadfish Festival.

[28] The sound of the vocalization has been likened to a chorus of kazoos, B-29s flying in formation,[28] an amplifier, a didgeridoo, "a drone of bees or maybe even the chanting of monks,"[30] and "an orchestra full of mournful, rasping oboes.

[3][32] This fish is an important prey for the bald eagle in some coastal areas, being the most common food provided to eaglets by their parents in one study on Vancouver Island.