Invemar

Santa Marta, Colombia

M. Eric Anderson, PhD

J. L. B. Smith Institute of Ichthyology

Grahmstown, South Africa

Eugene K. Balon, PhD University of Guelph Guelph, Ontario, Canada

George Benz, PhD Tennessee Aquarium Research Institute and Tennessee Aquarium Chattanooga, Tennessee

Tim Berra, PhD

The Ohio State University

Mansfield, Ohio

Ralf Britz, PhD Smithsonian Institution Washington, D.C.

John H. Caruso, PhD

University of New Orleans, Lakefront

New Orleans, Louisiana

Marcelo Carvalho, PhD

American Museum of Natural History

New York, New York

José I. Castro, PhD Mote Marine Laboratory Sarasota, Florida

Bruce B. Collette, PhD National Marine Fisheries Systematics Laboratory and National Museum of Natural History Washington, D.C.

Roy Crabtree, PhD Florida Fish and Wildlife Conservation Commission Tallahasee, Florida

Dominique Didier Dagit, PhD The Academy of Natural Sciences Philadelphia, Pennsylvania

Terry Donaldson, PhD University of Guam Marine Laboratory, UOG Station Mangliao, Guam

Michael P. Fahay, PhD NOAA National Marine Fisheries Service, Sandy Hook Marine Laboratory Highlands, New Jersey

John. V. Gartner, Jr., PhD St. Petersburg College St. Petersburg, Florida

Howard Gill, PhD Murdoch University Murdoch, Australia

Lance Grande, PhD

Field Museum of Natural History

Chicago, Illinois

Terry Grande, PhD Loyola University Chicago Chicago, Illinois

David W. Greenfield, PhD University of Hawaii Honolulu, Hawaii

Melina Hale, PhD University of Chicago Chicago, Illinois

Ian J. Harrison, PhD

American Museum of Natural History

New York, New York

Phil Heemstra, PhD South African Institute for Aquatic Biodiversity Grahamstown, South Africa

Jeffrey C. Howe, MA Freelance Writer Mobile, Alabama

Liu Huanzhang, PhD Chinese Academy of Sciences Hubei Wuhan, People's Republic of China

G. David Johnson, PhD Smithsonian Institution Washington, D.C.

Scott I. Kavanaugh, BS University of New Hampshire Durham, New Hampshire

Frank Kirschbaum, PhD Institute of Freshwater Ecology Berlin, Germany

Kenneth J. Lazara, PhD

American Museum of Natural History

New York, New York

Andrés López, PhD Iowa State University Ames, Iowa

John A. MacDonald, PhD The University of Auckland Auckland, New Zealand

Jeff Marliave, PhD

Institute of Freshwater Ecology

Vancouver, Canada

John McEachran, PhD Texas A&M University College Station, Texas

Leslie Mertz, PhD Wayne State University Detroit, Michigan

Elizabeth Mills, MS Washington, D. C.

Katherine E. Mills, MS Cornell University Ithaca, New York

Randall D. Mooi, PhD Milwaukee Public Museum Milwaukee, Wisconsin

Thomas A. Munroe, PhD National Systematics Laboratory Smithsonian Institution Washington, D.C.

Prachya Musikasinthorn, PhD Kasetsart University Bangkok, Thailand

John E. Olney, PhD College of William and Mary Gloucester Point, Virginia

Frank Pezold, PhD

University of Louisiana at Monroe

Monroe, Louisiana

Mickie L. Powell, PhD University of New Hampshire Durham, New Hampshire

Aldemaro Romero, PhD Macalester College St. Paul, Minnesota

Robert Schelly, MA

American Museum of Natural History

New York, New York

Matthew R. Silver, BS University of New Hampshire Durham, New Hampshire

William Leo Smith, PhD American Museum of Natural History and Columbia University New York, New York

Stacia A. Sower, PhD University of New Hampshire Durham, New Hampshire

Melanie Stiassny, PhD

American Museum of Natural History

New York, New York

Tracey Sutton, PhD Woods Hole

Oceanographic Institution Woods Hole, Massachusetts

Gus Thiesfeld, PhD Humboldt State University Arcata, California

Jeffrey T. Williams, PhD Smithsonian Institution Washington, D.C.

Contributing illustrators

Drawings by Michigan Science Art

Joseph E. Trumpey, Director, AB, MFA

Science Illustration, School of Art and Design, University of Michigan

Wendy Baker, ADN, BFA Brian Cressman, BFA, MFA Emily S. Damstra, BFA, MFA Maggie Dongvillo, BFA Barbara Duperron, BFA, MFA Dan Erickson, BA, MS Patricia Ferrer, AB, BFA, MFA

Maps by XNR Productions

Paul Exner, Chief cartographer XNR Productions, Madison, WI

Tanya Buckingham

Jon Daugherity

Gillian Harris, BA Jonathan Higgins, BFA, MFA Amanda Humphrey, BFA Jacqueline Mahannah, BFA, MFA John Megahan, BA, BS, MS Michelle L. Meneghini, BFA, MFA Bruce D. Worden, BFA

Thanks are due to the University of Michigan, Museum of Zoology, which provided specimens that served as models for the images.

Laura Exner Andy Grosvold Cory Johnson Paula Robbins

Polymixiiformes

(Beardfshes)

Class Actinopterygii Order Polymixiiformes Number of families 1

Photo: Beardfish (Polymixia berndti) live in deep marine waters, at 60-1,706 ft (18-520 m). They are rarely seen alive. This specimen was found near Oahu. (Photo by John E. Randall. Reproduced by permission.)

Photo: Beardfish (Polymixia berndti) live in deep marine waters, at 60-1,706 ft (18-520 m). They are rarely seen alive. This specimen was found near Oahu. (Photo by John E. Randall. Reproduced by permission.)

Evolution and systematics

Beardfishes of the order Polymixiiformes comprise a single living family, Polymixiidae, containing one genus, Polymixia, and, according to the revisional study of Kotlyar (1993), ten species. These seemingly nondescript fishes have a remarkably checkered taxonomic history, and few fishes have been shifted back and forth in different phylogenetic schemes as have these poorly understood animals. Although most systematists agree that Polymixiiformes are basal acan-thomorphs, their precise placement at the base of this huge radiation of spiny-rayed fishes remains a mystery. In view of the longstanding confusion regarding the phylogenetic position of beardfishes, it should be clear that the small size of the order is no indication of their evolutionary importance. Although the group is represented today by a single genus, the Polymixiiformes have a much more diverse fossil record, and at least two families, the Aipichthyidae and Polymixiidae, containing some six genera, are currently recognized.

Polymixiiforms appear first in the fossil record in the late Cretaceous period, some 95 million years ago, and have been viewed as being of considerable importance to our understanding of the spiny-rayed fishes and their evolution. In 1964 the noted British paleoichthyologist Colin Patterson reviewed polymixiiform fossil diversity and discussed the striking similarities between them and certain families of living perciforms such as carangids (jacks) and monodactylids (moonfishes). Whether these similarities reflect the common phenomenon of convergent evolution or are the result of recent common ancestry remains an open question. Whatever the case, such an ongoing confusion serves to highlight the importance of Polymixiiformes to our understanding of the evolution of spiny-rayed fishes.

Physical characteristics

Polymixia are rather deep-bodied fishes, with prominent blunt snouts and large eyes. Their dorsal and anal fins bear well-developed spines, but a spine is lacking in the subab-

dominally positioned pelvic fins, which have a single, segmented, leading ray and six branched rays. All beardfishes are characterized by the possession of a pair of hyoid barbels. These "chin" barbels are internally supported by three bran-chiostegal rays of the hyoid arch, and their characteristic appearance lends their bearers the name "beardfishes." A 2001 study by Kim and his colleagues highlights the unique nature of the anatomy and muscular control of beardfish barbels.

Distribution

Beardfishes are known to occur in the Atlantic, Indian and Western Pacific oceans, as well as in tropical and subtropical waters. Worldwide collection data for Polymixia species are poor, and sampling in many regions is limited or nonexistent. When caught, most species are taken at depths ranging from 492-2,132.5 ft (150-650 m), but catches from as shallow as 164 ft (50 m) have been recorded.

Habitat

Very little is known of the habitat preferences of Polymixia species, but the presence of chin barbels suggests a bottom-dwelling mode of life, probably over sandy or muddy substrates.

Behavior

Nothing is known.

Feeding ecology and diet

The stomach of Polymixia is thick walled and muscular, often with over 100 pyloric ceca (pouches). Analyses of the gut contents indicate an opportunistic diet of crustaceans, squid, and small fishes. Interestingly, beardfishes are recorded among the stomach contents of the Indian Ocean coelacanths, as well as in those of a wide range of other fish predators.

Reproductive biology

Polymixia eggs are unknown, and the smallest individual so far identified is a 0.15 in (0.39 cm) postflexion larva, which was described in some detail by Konishi and Okiyama, who noted the presence of moderately developed head spination similar to that found in many beryciform fishes. Reproductive biology is virtually unknown, but sexual dimorphism in coloration has been noted in P. lowei, where an intense black marking on the anal fin and both lobes of the tail fin are present only in male fish.

Conservation status

None of the Polymixia species are included on the IUCN Red List. Although catches of some species are relatively high in some regions, there are no indications of overfishing.

Significance to humans

Beardfishes are marketed for human consumption in most regions; however, commercial catches are limited but growing. As catches of other species have declined, a number of Pacific beardfish species have been tagged as having unex-ploited fisheries potential.

Species accounts

Stout beardfish

Polymixia nobilis

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