The Midshipman fishes are the genusPorichthys of toadfishes. 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 fishes, 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 fishes 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.
There are about 15 species of midshipman fishes, including the following:
Atlantic Midshipman Porichthys plectrodon
Daisy Midshipman Porichthys margaritatus
Darkedge Midshipman Porichthys analis
Greene's Midshipman Porichthys greenei
Mimetic Midshipman Porichthys mimeticus
Plainfin Midshipman, Humming Toadfish, or California Canary Fish Porichthys notatus
Saddle Midshipman Porichthys ephippiatus
Smalleye Midshipman Porichthys oculellus
Specklefin Midshipman Porichthys myriaster
Porichthys bathoiketes
Porichthys kymosemeum
Porichthys oculofrenum
Porichthys pauciradiatus
Porichthys porosissimus
Porichthys queenslandiae
External links
FishBase list of species in the genus, with links (http://www.fishbase.org/NomenClature/ScientificNameSearchList.cfm?Crit1_FieldName=SYNONYMS.SynGenus&Crit1_FieldType=CHAR&Crit1_Operator=EQUAL&Crit1_Value=porichthys&Crit2_FieldName=SYNONYMS.SynSpecies&Crit2_FieldType=CHAR&Crit2_Operator=contains&Crit2_Value=&group=summary&backstep=-2)
News story about the humming toadfish (http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/07/19/MNGFK7N32O1.DTL&type=printable)
References
Sisneros, J. A., Forlano, P. M., Deitcher, D. L., & Bass, A. H. (2004). Steroid-dependent auditory plasticity leads to adaptive coupling of sender and receiver. Science, 305, 404-407.
The Midshipmanfishes are the genus Porichthys of toadfishes.
Typical midshipmanfishes, such as the Plainfin Midshipman, are nocturnal and bury themselves in sand or mud of the intertidal zone during the day.
Mating in midshipmanfishes 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.
Midshipman have a second group of smaller, "type II" males that do not acoustically court females but rather sneak into a nest while females are there with a type I male (4).
The vocal motor system of teleost fishes such as midshipman has provided a powerful model for such studies because the physical attributes of their acoustic signals can be understood in terms of the electrical activity of the nervous system.
Hence, one explanation for how individual midshipmanfish choose one of two concurrent hum-like signals that form an acoustic beat is that they have neurons with temporal coding properties that permit the segregation and discrmination of the fine temporal structure of single and concurrent hums.
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