Fishes: A Guide to Their Diversity. Philip A. Hastings
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ACIPENSERIFORMES : ACIPENSERIDAE—Sturgeons
DIVERSITY: 4 genera, 26 species
REPRESENTATIVE GENERA: Acipenser, Huso, Pseudoscaphirhynchus, Scaphirhynchus
DISTRIBUTION: Northern Hemisphere temperate (except Greenland)
HABITAT: Anadromous or freshwater; temperate; demersal to benthic on soft bottoms
REMARKS: Five rows of bony scutes along the body distinguish sturgeons from all other fishes. These large freshwater/anadromous fishes inhabit lakes, slow-moving rivers, and coastal areas and feed on mollusks, crustaceans, insect larvae, and occasionally plants. The long-lived species of the genus Huso are some of the largest freshwater fishes in the world, reaching 8 m TL and over 1,500 kg, and are the source of what is considered the world’s finest caviar. As a result of the caviar fishery and habitat destruction, nearly all sturgeons are vulnerable to extinction and at least 16 species are listed as critically endangered by the IUCN (2013).
REFERENCES: Bemis et al., 1997; Birstein et al., 2002; Boschung and Mayden, 2004; Choudhury and Dick, 1998; Grande and Bemis, 1996; Hilton et al., 2011; Hochleithner and Gessner, 2001; IUCN, 2013.
ACIPENSERID CHARACTERISTICS:
1) five rows of bony scutes along body
2) four oral barbells
3) caudal fin heterocercal
4) gular plates absent
5) teeth absent in adults
6) pectoral fin with soft rays fused into an anterior spine-like element
7) skeleton largely composed of cartilage
ILLUSTRATED SPECIMEN:
Acipenser medirostris, SIO 62–155, 960 mm TL (lateral and dorsal views).
ACIPENSERIFORMES : POLYODONTIDAE—Paddlefishes
DIVERSITY: 2 genera, 2 species
REPRESENTATIVE GENERA: Polyodon, Psephurus
DISTRIBUTION: Mississippi River and Yangtze River basins
HABITAT: Freshwater but can tolerate some salinity; temperate; pelagic in slow-moving rivers
REMARKS: Paddlefishes are large (up to 3 m in length, with reports of much larger specimens), riverine species characterized by a long spatula-like snout. Although similar in appearance to its Chinese counterpart, the American Paddlefish is planktivorous with a non-protrusible mouth and numerous, long gill rakers, while the Chinese Paddlefish eats other fishes, has a protrusible mouth, and fewer, shorter gill rakers. Both species, however, use their paddles for electroreception in murky river waters (Wilkens et al., 2002). As a result of habitat destruction, pollution, and overfishing, the Chinese Paddlefish is critically endangered and may be extinct (IUCN, 2013; Zhang et al., 2009).
REFERENCES: Boschung and Mayden, 2004; Grande and Bemis, 1991, 1996; Inoue et al., 2003; IUCN, 2013; Wilkens et al., 2002; Zhang et al., 2009.
POLYODONTID CHARACTERISTICS:
1) snout long, flat, paddle-like
2) body essentially naked, with few scales
3) spiracle above and behind eye
4) caudal fin heterocercal
5) gill cover extended posteriorly
6) snout and gill cover with conspicuous electrosensory pores
ILLUSTRATED SPECIMEN:
Polyodon spathula, TU 37062–7, 882 mm TL (lateral and dorsal views)
HOLOSTEI—Gars and Bowfins
The Holostei includes the gars, with seven extant species, and the single extant species of bowfin. This group was recognized in early classifications of fishes (e.g., Patterson, 1973), but for a number of years, the Holostei was thought to be a paraphyletic group, with the bowfin more closely related to the teleost fishes. However, a recent exhaustive study of extant and fossil species by Grande (2010) provides morphological support (e.g., presence of a paired vomer) for the monophyly of the Holostei, in agreement with several analyses of molecular data (Inoue et al., 2003; Meyer and Zardoya, 2003). The Holostei is the sister group of the Teleostei; together they are called the Neopterygii.
LEPISOSTEIFORMES : LEPISOSTEIDAE—Gars
DIVERSITY: 1 family, 2 genera, 7 species
REPRESENTATIVE GENERA: Atractosteus, Lepisosteus
DISTRIBUTION: North America and Cuba
HABITAT: Freshwater to coastal marine; tropical to temperate; pelagic in rivers, lakes, and estuaries
REMARKS: Gars are elongate, toothy fishes that live predominantly in freshwater or brackish water and feed on other fishes, some benthic invertebrates, and waterfowl. Several small, toothed bones (including the infraorbitals) form the upper jaw. Gars use their lung-like gas bladders to supplement respiration (Graham, 1997) and are known to spend time in a stationary position near the surface. Opisthocoelous vertebrae (anterior end convex, posterior end concave) are unique to this group, one genus of the Blenniidae, and some reptiles.
REFERENCES: Boschung and Mayden, 2004; Graham, 1997; Grande, 2010; Wiley, 1976; Wiley, in Carpenter, 2003.
LEPISOSTEIFORM CHARACTERISTICS:
1) elongate jaws with fanglike teeth
2) bony, ganoid scales in oblique rows
3) row of median scales along the first ray of the dorsal, anal, and caudal fins
4) body elongate, with the dorsal and anal fins located posteriorly
5) pectoral fins low on body, pelvic fins abdominal
6) cheek with numerous bony plates
7) three branchiostegal rays
ILLUSTRATED SPECIMEN:
Atractosteus spatula, TU 124963, 666 mm TL (lateral and dorsal views)
AMIIFORMES : AMIIDAE—Bowfins
DIVERSITY: 1 family, 1 genus, 1 species
REPRESENTATIVE GENUS: Amia
DISTRIBUTION: Eastern North America
HABITAT: Freshwater in streams, rivers, and swamps; temperate; demersal over soft bottoms
REMARKS: The Bowfin, Amia calva, is the only living representative of the Amiidae and Amiiformes. It is restricted to eastern North America, though fossil forms are known worldwide (Grande and Bemis, 1999). It inhabits still or slow-moving freshwaters and can swim by either undulating its long dorsal fin or utilizing its strong tail. The Bowfin is predatory and feeds on other fishes, reptiles, amphibians, birds, snails, and crayfishes. It is among the many groups of air-breathing fishes and utilizes its lung-like gas bladder to supplement respiration (Graham, 1997). Males construct a nest where they defend eggs and young after they hatch.
REFERENCES: Boschung and Mayden, 2004; Graham, 1997; Grande and Bemis, 1998, 1999.
AMIIFORM CHARACTERISTICS:
1) body cylindrical, with long dorsal fin
2)