Pisces (zoology) - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/pisces-zoology/519700

Article by: Bailey, Reeve M. Formerly, Division of Fishes, Museum of Zoology, University of Michigan, Ann Arbor, Michigan. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097-8542.519700 (http://dx.doi.org/10.1036/1097-8542.519700)

Content

Number of recent species Economics Additional Readings Ecology

A term that embraces all fishes and fishlike vertebrates. In early zoological classifications fishes, like mammals, birds, reptiles, and amphibians, were ranked as a class of the vertebrates. As knowledge of fishes increased, it became apparent that, despite their common possession of gills and fins and their dependence on an aquatic environment, not all fishes were closely related. At least five groups of fishes with modern descendants were already established before the tetrapods appeared. Not only are these groups older, but some are decidedly more divergent structurally than are the four classes of tetrapods. For these reasons several classes of fishes are now recognized. The number of classes varies; one reputable but extreme classification recognizes 11 classes of fishes.

The primary cleavage in vertebrate classification is that separating the jawless fishes, or Agnatha, from those vertebrates with jaws, the Gnathostomata. After recognition of this split, the name Pisces was commonly restricted to the jawed fishes. When these in turn were divided into two or more classes, Pisces was further restricted by some authorities to the bony fishes. Another scheme involves assignment of class names to each of the major constituent groups of jawed fishes, and use of Pisces as a superclass name. In view of the confusion, it seems best to revert to early practice and to employ Pisces as a group name of convenience to embrace all classes of fishlike vertebrates, from jawless fishes to bony fishes. In this sense it has no actual taxonomic status because it cuts across natural classification, dividing the gnathostomes and grouping part of them with the agnaths. See also: Gnathostomata (/content/gnathostomata/293800); Jawless vertebrates (/content /jawless-vertebrates/014900)

The Pisces include four well-defined groups that merit recognition as classes: the Agnatha or jawless fishes, the most primitive; the Placodermi or armored fishes, known only as Paleozoic fossils; the Chondrichthyes or cartilaginous fishes; and the Osteichthyes or bony fishes. Future research may demonstrate the need for further division, but this is most likely to involve Paleozoic groups. See also: Chondrichthyes (/content/chondrichthyes/133100); Osteichthyes (/content /osteichthyes/478500); Placodermi (/content/placodermi/520900)

Number of recent species

Present fish classification is not sufficiently precise to permit an accurate tabulation of the number of living species. New kinds are constantly being discovered, others are being synonymized as the result of new research, and the literature is scattered. Nevertheless, estimates by competent ichthyologists are so diverse, ranging from 18,000 to 40,000, that an effort is here made to arrive at a reasonably acceptable approximation. There is indication that most previous estimates are too high.

1 of 4 8/12/2015 10:19 AM Pisces (zoology) - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/pisces-zoology/519700 Counts for Recent groups and species include Agnatha, 2 families, about 11 genera, and approximately 45 species; Chondrichthyes, 31 families, some 132 genera, and roughly 575 species; and Osteichthyes, 32 orders, about 357 families, 3570 genera, and about 17,600 species. This last figure broken down gives about 5100 species in 29 orders, nearly 2000 species in the Siluriformes, 3000 species in the Cypriniformes, and 7500 species in the Perciformes. It is to be emphasized that the classification of many groups, especially those in the deep seas and in the tropics, is imperfectly known. Thus, further study will permit refinement of this enumeration of just under 18,300 recognized species of Recent fishes.

Ecology

Fishes live in almost all permanent waters to which they have been able to gain access. In general they have evolved a body conformation and specialized features that adapt them harmoniously to the world about them. Inhabitants of mountain torrents may have peculiar attachment organs; those living in Antarctic waters at a temperature below freezing have made needed physiological adjustments; fishes of the deep sea commonly carry their own light source, and the female anglerfish is assured a mate by the parasitism of the male on her body. In the East Indies some fishes skip with ease over mud flats, and others undertake nightly forays on land. Some fishes mature at extremely small size. A Philippine goby, Mistichthys, reaches a length of only 0.5 m (1.25 cm) and is commercially important as a food fish although it takes 31,500 fish to make 1 lb (70,000 fish to make 1 kg); and a Samoan fish, Schindleria, attains a weight of only 6 mg. At the other extreme, the whale shark is reputed to reach a length of 60 ft (20 m), and a 38-ft (13 m) individual weighed more than 13 tons (11.7 metric tons).

Adaptive radiation

Because their bodies are supported by water, fishes have been afforded the luxury of diversification in body form not possible for terrestrial animals. A deep, pancake-thin body is not uncommon, and an eellike form has been independently developed in many phyletic lines. Trunkfishes are enclosed in a boxlike casque, and some deep-sea fishes have eyes at the tips of elongate stalks. Long, trailing fins are frequent; sargassum fishes develop appendages that serve as holdfasts and for concealment.

Food habits

Most fishes are more or less carnivorous and predatory, but there is wide diversity in food habits. Many fishes have numerous slender gill rakers with which they strain microorganisms from the water; others have massive teeth and strongly muscled jaws to aid in crushing mollusks or crustaceans. Browsers, nibblers, and grazers employ specially adapted teeth and jaws to scrape vegetation or small attached animals. Some wrasses pluck parasites from larger fishes, and lampreys parasitize other fishes.

Reproductive habits

Reproductive habits are no less varied than feeding behavior. Most fishes are oviparous and scatter their eggs, but nest building and parental care assume a broad spectrum—from a prepared pile of pebbles, through a grassy spherical retreat, to oral incubation or development of a marsupial pouch on the underside of the male pipefish. Viviparity and ovoviviparity have originated along independent lines. Enormously complicated modifications of the anal fin have been evolved to effect insemination of some species in which the young are born alive.

Economics

Fishes play an important role in the lives of most people. Fishing is a way of life in most primitive cultures, and ranks high among recreational activities in highly civilized peoples. Maintenance and care of home aquarium fishes provide an avocation for probably millions of people. An occasional swimmer is killed by sharks; more people die from ciguatera contracted from eating poisonous fish flesh; and venomous fishes take a limited toll in human life and suffering. See also: Chordata (/content 2 of 4 8/12/2015 10:19 AM Pisces (zoology) - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/pisces-zoology/519700 /chordata/133700); Vertebrata (/content/vertebrata/730900)

Reeve M. Bailey

Additional Readings

E. V. Balian et al. (eds.), Freshwater Animal Diversity Assessment, Springer, Dordrecht, Netherlands, 2008

M. Bradford, F. J. Kroon, and D. J. Russell, The biology and management of Tilapia mariae (Pisces, Cichlidae) as a native and invasive species: A review, Mar. Freshwater Res., 62(8):902–917, 2011 DOI: 10.1071/MF10289 (http://dx.doi.org/10.1071 /MF10289)

D. L. Felder, Gulf of Mexico Origin, Waters, and Biota: Biodiversity, Texas A&M University Press, College Station, TX, 2009

D. J. Russell, P. A. Thuesen, and F. E. Thomson, A review of the biology, ecology, distribution and control of Mozambique tilapia, Oreochromis mossambicus (Peters 1852) (Pisces, Cichlidae) with particular emphasis on invasive Australian populations, Rev. Fish Biol. Fisher., 22(3):533–554, 2012 DOI: 10.1007/s11160-011-9249-z (http://dx.doi.org/10.1007 /s11160-011-9249-z)

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