Ostariophysi
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Gonorynchiformes |
Ostariophysi is a superorder of fish. Members of this superorder are called ostariophysans. This diverse group contains almost 8,000 species, about 28% of known fish species in the world and 68% of freshwater species, and are present on almost all major continents except Antarctica. They have a number of common characteristics such as an alarm substance and a Weberian apparatus.[1] Members of this group include fish important to people for food, sport, the aquarium industry, and research.
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[edit] Classification
Currently, this superorder is divided into two series, Anotophysi and Otophysi. However, in older literature, Ostariophysi was restricted only to the fish that are currently classified under Otophysi.[1] Otophysi was coined in 1970 by Rosen and Greenwood to separate the traditional Ostariophysans from the added Gonorynchiformes.[2]
The superorder is classified below:
- Series Anotophysi
- Gonorynchiformes - about 37 species
- Series Otophysi
- Cypriniformes (minnows and allies) - about 3,268 species (contains Cyprinidae, largest family of freshwater fishes)
- Characiformes (characins and allies) - at least 1,674 species
- Siluriformes (catfishes) - about 1,727 species
- Gymnotiformes (electric eels, American knifefishes) - at least 173 species (sometimes grouped under Siluriformes)
[edit] Diversity
Ostariophysans includes fiver major lineages and is a very diverse group. As of 2006 (Nelson), the five orders contain 1,075 genera and about 7,931 species, which is about 28% of all known fish species. The four largest families in this group (Cyprinidae, Characidae, Loricariidae, and Balitoridae) include 4,656 species, over half (59%) of Ostariophysan species. Ostariophysians account for about 68% of all freshwater species; in fact, there are only about 123 marine species (Chanidae, Gonorynchidae, most Ariidae, about half of Plotosidae). They are present on all continents and major land masses except Antarctica, Greenland, and New Zealand.[1]
This group includes a wide variety of different fishes. It contains the largest freshwater fish ever caught, the Mekong giant catfish, which can weigh up to about 300 kg.[3] It also contains the smallest species of freshwater fish, Danionella translucida at only 12 mm in length.[1] Some of these fish are able to breathe atmospheric oxygen (Clariidae) or even live out of water (Phreatobius cisternarum).[4] Some Ostariphysans have the ability to produce electricity (Malapteruridae, Gymnotiformes).
[edit] Physical characteristics
Most species possess a swim bladder (except in Gonorynchus). The swim bladder is usually divided into two chambers. A smaller anterior chamber is partially or completely covered by a silvery peritoneal tunic. A larger posterior chamber may be reduced or absent in some groups. Minute, unicellular, horny projections known as "unculi" are commonly present on various body parts and are only known from ostariophysans.[1]
Many Ostariophysans have the characteristic of an alarm substance that is part of a fright reaction. This is a pheromone produced in epidermal club cells and is similar or identical in all ostariophysians. When the fish is injured, this pheromone is released; other fish of the same species or similar species can smell this pheromone, causing a fright reaction. However, some fish possess the alarm substance without the fright reaction or lack both the alarm substance and the fright reaction to the alarm substance.[1]
[edit] Weberian apparatus
In Otophysans, one of the main characteristics is the Weberian apparatus. It is made up of a set of bones known as Weberian ossicles, a chain of small bones that connect the auditory system to the gas bladder of fishes.[1] The ossicles connect the gas bladder wall with Y-shaped lymph sinus that abuts the lymph-filled transverse canal joining the sacculi of the right and left ears. This allows the transmission of vibrations to the inner ear.
In anotophysans, the three first vertebrae are specialized and associated with one or more cephalic ribs (a primitive Weberian apparatus). In the otophysians a distinct modification of the anterior four or five first vertebrae is found as well as the Weberian ossiciles.[1]
The fully functioning Weberian apparatus consists of the swim bladder, the Weberian ossicles, a portion of the anterior vertebral column, and some muscles and ligaments. It is named after the German anatomist and physiologist Ernst Heinrich Weber who first described the Weberian ossicles.[1]
[edit] References
- ^ a b c d e f g h i j Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc.. ISBN 0471250317.
- ^ Ostariophysi. Tree of Life Web Project. Retrieved on 2007-03-26.
- ^ Grizzly Bear-Size Catfish Caught in Thailand. National Geographic News. Retrieved on 2006-07-14.
- ^ Froese, R. and D. Pauly. Editors.. Species Summary: Phreatobius cisternarum. FishBase. Retrieved on 2006-11-26.
