The Midshipman fish are the genus Porichthys of Toadfish. They are distinguished by having photophores (which they use to attract prey and after which they are named, reminding some of a naval uniform’s buttons) and four lateral lines. Typical Midshipman fish, such as the Plainfin Midshipman, are nocturnal and bury themselves in sand or mud of the intertidal zone during the day. At night they float just above the seabed. Some species are armed with venomous dorsal spines and are capable of inflicting serious injuries if handled.
Mating in Midshipman fish depends on auditory communication; males during the breeding season broadcast a sound usually described as a hum, generated by rapid contractions of the muscles in the swim bladder. The sound can be kept up for up to an hour, and is loud enough to be heard by (and to puzzle) people on nearby land and houseboats; the hulls of the boats tend to amplify the sound to sleep-disrupting levels. Reproductive females develop a selective sensitivity to this sound, and respond by laying eggs in the rock nest of a singing male.
Researchers from the University of Washington and Cornell University have recently demonstrated that the increase in sensitivity associated with female reproductive status can be duplicated in non-reproductive females of the Plainfin Midshipman (Porichthys notatus) by boosting hormone levels, and that this acts on the fish’s inner-ear to produce the change in sensitivity. An increase in levels of the hormones testosterone and estradiol triggers changes that result in increased sensitivity to higher sound frequencies.