Porichthys plectrodon Jordan and Gilbert 1882
Atlantic midshipman

The species has been commonly referred to P. porosissimus Valenciennes 1837.

Some XIX and early XX Century accounts place the species in the genus Nautopaedium.

DESCRIPTION

Shares with other members of the Batrachoididae three pairs of gills; gill membrane broadly joined to isthmus; six branchiostegal rays; no pyloric caeca, ribs, epiotics, or intercalars; peculiar intervertebra-like basal articulation of upper hypurals with rest of caudal skeleton; jugular pelvic fins (Nelson, 1994).

Dorsal spines (total): 2-2; Dorsal softrays (total): 35-36; Anal spines: 0-0; Anal soft-rays: 32-33. Branchiostegal photophore series restricted mid-ventral, with deep U-shaped apex anteriorly; margin of soft dorsal fin membranes with black blotches, black margin intermittent. Body elongated, tapered; eyes widely separated, protrusible; rows of photophores on ventral surface arranged rather like the buttons on an XIX Century naval midshipman's uniform (hence the common name), second row V-shaped (Hoese and Moore, 1998).

DISTRIBUTION

P. plectrodon occurs in the Atlantic from Virginia to Brazil (Hoese and Moore, 1998) (the very similiar P. porosissimus with which this species has been confused, occurs off South America from Brazil to Argentina (Gilbert and Kelso, 1971)).

LIFE HISTORY AND ECOLOGY

Generally found on sand or mud bottoms mostly in depths of ten to two hundred fifty meters (5). Experiments in aquaria have shown that P. plectrodon prefers mud to sand bottoms. P. plectrodon is found in a wide variety of salinities and temperatures, but tends to avoid extremes (Lane, 1967, Moore 1970b).

Analysis of stomach contents of specimens of P. plectrodon showed their diet to consist of primarily amphipods, mysids, and striped anchovies, Anchoa hepsetus (Lane, 1967).

Spawning occurs in three main peaks for the population; the spring and summer peaks are in the bays, and the fall peak is in the Gulf of Mexico (Lane, 1967). Males are believed to build a nest, perhaps little more than a patch of oyster shell which is kept clear of mud and fine sediment. The males probably use their photophores as well as vocalizations to attact females and to defend their territories for other males. Spawning itself is rather rough, the male grabbing the female by the jaw and holding her in the nest until spawning is finished (Moore, 1970a).

Adhesive eggs are layed by the females attached to the oyster shells or other hard substrate within the nest. The emerging larvae are approximately eight millimeters in total length and remain attached to the substrate by an adhesive disk at the base of the yolk sac. The male continues to guard the nest until the larvae are free swimming (Moore, 1970a). The free swimming larvae develop quickly and settle on the soft bottom, burying themselves. The juveniles are exceptionally tolerant of low salinity and are occasionally found in freshwater or very low salinity water(Lane, 1967).

Because of the high mortality associated with spawning, almost all adults live no more than one year. Males of Porichthys frequently become emaciated after spawning due to their constant guarding and aerating the eggs and consequently suffer high mortality. Females of P. plectrodon caught after the spawning season tend to be in very poor condition and are believed to all die as no two year old females have ever been recorded (Lane, 1967).

Spawning of the related species P. notatus occurs from April to August in the intertidal zone where males excavate nests under rocks and other solid structures (Plainfin Midshipman ). After courtship, females deposit adhesive eggs in the nest and the resident male fertilizes them. The emerging larvae are seven to eight millimeters in total length and attach to nearby rocks via an adhesive disk at the base of the yolk sac.

Adults of P. plectrodon (Lane, 1967) and P. notatus (Wang, 1986) remain buried on the bottom during the day and rise in the water column at night to feed. This behavior in P. plectrodon has been shown to be in response to light. The act of burrowing into the mud begins by resting on the substrate and moving the anal and caudal fin from side to side and the small pelvics in a paddle-like motion. Movement of the large pectorals and gulping with the branchiostegals clear mud away from the head. As the fish sinks into the substrate, the dorsal fin is used to completely cover the dorsal surface with mud. The entire sequence is completed within three seconds. The eyes are usually left above the surface (Lane, 1967). Aside from seasonal migrations, batrachoidids are relatively sedentary and do not spend much time actively foraging for food. Feeding Behavior: Batrachoidids are typically sit and wait predators. They hide amongst debris or vegetation or remain buried until a prey item passes before them. They then dart out and grasp their prey. P. plectrodon is also capable of filter feeding for microcrustaceans and larval fish and is equipped with numerous long gill rakers for this purpose (Lane, 1967).

The male mating call is characteristic of both Opsanus and Porichthys and is produced by rapid contractions of the muscles surrounding the swim bladder. The sound producing muscles of O. tau contract at approximately two hundred Hz and are the fastest vertebrate muscles known (Rome, 1996, Fine et al., 2001). Those of P. notatus contract at about one hundred Hz and produce a humming two to three decibels above ambient sound (McCosker, 1983). Aside from their use by males in long duration calls (up to fifteen minutes), they are used by both sexes for assorted short duration grunts and growls not associated with reproduction.

P. plectrodon possesses poisonous opercular spines. These are grooved dorsally and have a poison gland at the base. In humans, the poison causes a warm sensation followed by intense pain lasting about fifteen minutes. The pain subsides slowly during the next fifteen minutes. Experiments have shown that when predators attack these fish they immediately spit them out injured but usually alive. The photophores are flashed to warn off potential predators. P. plectrodon is rarely found in the stomachs of other fishes (Lane, 1967). Batrachoidids are cryptic fishes and often avoid predation by blending in with their surroundings or by burrowing into the bottom.

CONSERVATION STATUS

The species is not fished commercially or recreationally, at least not intentionally. However, it commonly occurs as part of the by-catch in commercial shrimp trawls. Because they lack scales, midshipmen are not kosher (Atz, 1997).

REFERENCES

Atz, J. W., 1997. Non-Kosher Fish: http://www.kashrus.org/kosher/non_kosh.html

FishBase website www.fishbase.org/Nomenclature/NominalSpeciesList.cfm?family=Batrachoididae

Fine, M. L., K. L. Malloy, C. B. King, S. L. Mitchell, and T. M. Cameron, 2001. Movement and sound generation by the toadfish swimbladder. J. Comp. Physiol. A DOI 10.1007/s003590100209 Available through On-line First at: http://link.springer.de/link/service/journals/00359/contents/01/00209/s003590100209ch002.html

Gilbert, C. R. 1968. Western Atlantic batrachoidid fishes of the genus Porichthys, including three new species. Bull. Mar. Sci. 18: 671-730.

Gilbert, C. R. and K. P. Kelso, 1971. Fishes of the Tortugero area, Caribbean Costa Rica. Bull. Fla. St. Mus. Biol. Sci.16(1): 1 -54.

Hoese, H. D. and R. H. Moore, 1998. Fishes of the Gulf of Mexico: Texas, Louisiana and Adjacent Waters. Texas A&M University Press, College Station. 422 pp

Lane, E. D. 1967. A Study of the Atlantic Midshipman, Porichthys porosissimus, in the vicinity of Port Aransas, Texas. Contr. mar. Sci. Univ. Texas, 12: 1-53.

McCosker, J. E. 1986. In sum, it was some hum. Discover. June(1986): 66-71.

Moore, Richard H. 1970a. Observations on the nest guarding activities of the male Atlantic midshipman, Porichthys porosissimus Copeia (1) 196 - 197.

Moore, Richard H. 1970b. Diurnal variations in the activity and metabolism of the Atlantic Midshipman, Porichthys porosissimus. Contrib. mar. Sci. Univ. Texas, 15:33-43.

Nelson, J. S., 1994: Fishes of the world. 3rd Ed. -- John Wiley & Sons, Inc., New York. xx-600.

Rome, L. C., D. A. Syme, S. Hollingsworth, S. L. Lindstedt, and S. M. Baylor, 1996. The whistle and the rattle: the design of sound producing muscles. Proc. Natl. Acad. Sci. USA. 93:8095-8100. available on-line at at the PNAS web site http://www.pnas.org/cgi/content/abstract/93/15/8095?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=Rome&searchid=QID_NOT_SET&stored_search=&FIRSTINDEX=0&fdate=1/1/1996.

Wang, J. C. S., 1986. Plainfin Midshipmen (Porichthys notatus) in Fishes of the Sacramento-San Joaquin Estuary and Adjacent Waters, California: A Guide to the Early Life Histories. Technical Report 9 (FS/B10-4ATR 86-9) Berkeley Digital Library Project   http://elib.cs.berkeley.edu/kopec/tr9/html/sp-plainfin-midshipman.html