Atheriniformes

(vertebrate zoology) An order of actinopterygian fishes in the infraclass Teleostei, including flyingfishes, needlefishes, killifishes, silversides, and allied species.

(Rainbowfishes and silversides)

Class: Actinopterygii

Order: Atheriniformes

Number of families: 8

Evolution and systematics

The order Atheriniformes originally was conceived by Donn Rosen in 1964 to include the exocoetoids (flying fishes and allies), scomberesocoids (sauries), adrianichthyoids (ricefishes), cyprinodontoids (killifishes and allies), atherinoids (silversides and allies), and phallostethoids (priapium fishes). Today this disparate assemblage of fishes still is thought to be a natural group, but it has been parceled into three orders. Now called the Atherinomorpha, the group contains the orders Cyprinodontiformes and Beloniformes (put together as Division II atherinomorphs by Rosen and Parenti in 1981) and the Atheriniformes (Division I atherinomorphs according to Rosen and Parenti). Characters of the testis, egg, embryo, rostral cartilage and skull, and dorsal gill arch skeleton, among others, unite the Atherinomorpha. This chapter concerns the Atheriniformes, which at present includes the silversides, phallostethids, rainbowfishes, and related taxa.

At more than 50 million years old, fossils of the genus Atherinidarum from the early Eocene of France are the oldest known atheriniforms. Researchers disagree about the identity of the most basal atheriniform lineages and have variously proposed both freshwater (bedotiids and melanotaeniids) and partly or wholly marine (atherinopsids and notocheirids) groups. Through the course of their evolution different groups of atheriniforms have repeatedly breached the marine-freshwater barrier. Such an ability to colonize patchily distributed freshwater habitats has fostered speciation within the order, especially in the Americas and Australia. At present there are about 315 species and 49 genera of atheriniforms known to science.

Ichthyologists disagree on whether the Atheriniformes are a monophyletic group, descended from a single branch on the atherinomorph tree, or a hodgepodge of lineages on multiple branches that are associated closely with the Cyprinodontiformes and Beloniformes (which are considered sister groups). Even the number and constitution of families is in dispute: recent classifications have cited from six to ten families. In light of the disagreement in the literature, this treatment follows Joseph Nelson's book Fishes of the World, in which eight families are recognized within the order: Bedotiidae (Malagasy rainbowfishes), Melanotaeniidae (rainbowfishes), Pseudomugilidae (blue-eyes), Telmatherinidae (Sulawesi rainbows), Atherinidae (silversides), Notocheiridae (surf silversides), Dentatherinidae (pygmy or tusked silverside), and Phallostethidae (priapium fishes).

In 1996, the most recent treatment of the issue, Dyer and Chernoff marshaled 10 morphological characters supporting the Atheriniformes as a monophyletic, or natural, group. In addition, they proposed a new classification for the order, in which the number of families was reduced to six. Familial allocations within this new classification are in stark contrast to Nelson's scheme. Differences include an expansion of the family Melanotaeniidae to subsume the families Bedotiidae, Pseudomugilidae, and Telmatherinidae; an expansion of the family Phallostethidae to include Dentatherinidae; and an elevation of the Old World silverside genus Atherion to family status (Atherionidae). Furthermore, in agreement with a 1994 article by Saeed and collaborators, the New World silverside subfamilies Menidiinae and Atherinopsinae are shunted from the family Atherinidae into their own family, Atherinopsidae. Dyer and Chernoff's morphology-based hypothesis awaits further testing, especially using DNA sequence data. It is too soon to say whether their proposal will gain wide acceptance. Certainly, though, theirs will not be the last word on atheriniform relationships.

Physical characteristics

A reasonable degree of morphological diversity is found among the Atheriniformes, and, in particular, phallostethids exhibit a form that is unique among all fishes. The typical silverside generally is elongate and laterally compressed, with two dorsal fins, a single anal fin spine, usually cycloid scales, and no lateral line. Most are silvery in color and have a prominent mid-lateral stripe along each side of the body. Melanotaeniids are constructed similarly but often are deeper bodied and have sexually dimorphic color patterns. Male rainbowfishes frequently are brilliantly colored, with complex patterns, in various shades of red, yellow, orange, blue, and green. In telmatherinids, as well as some pseudomugilids and melanotaeniids, the anal and dorsal fins sometimes are elongated into filamentous extensions or elaborate fanlike shapes.

Most noteworthy among atheriniforms, however, are the extraordinarily modified phallostethids (priapium fishes). In both male and female phallostethids, the anal and genital openings are shifted anteriorly and are located under the throat. Males have an elaborate, bilaterally asymmetric copulatory structure under the head, called a priapium, for which no parallel exists among other fishes. A suspensory component of the priapium is made up of modified anterior pleural ribs and pelvic bones. Emerging from the posterior end of the priapium and arching forward almost the entire length of the head are the ctenactinia—elongate, curved bones used for clasping the female during mating. In different species, the anus is offset to one or the other side of the priapium, and the seminal papilla is offset opposite the anus. Both open anteriorly. The seminal papilla, which is elaborated into a copulatory organ in some species, is used to transfer bundles of sperm to the female.

Distribution

The Atheriniformes are distributed in mainly coastal areas of tropical and temperate seas throughout the world and also occur in freshwater lakes and streams in many regions. Largely or entirely marine atheriniform families include the Atherinidae, Notocheiridae, and Dentatherinidae. Atherinids occur worldwide in near-shore marine environments and in freshwaters of primarily the Americas and Australia. Members of the atherinid subfamily Menidiinae show a propensity for invasion of freshwater habitats from coastal marine environments. In the lakes and streams of the Mesa Central of southern Mexico, freshwater menidiines have diversified into a species flock of 20 or so closely related species with exceedingly circumscribed ranges (many are found in only a single lake). Notocheirids are exclusively marine: five species of the genus Iso are distributed along the coasts of South Africa, India, Japan, Australia, and Hawaii, and the species Notocheirus hubbsi is found only along the coast of Chile. Finally, the family Dentatherinidae consists of but a single species, Dentatherina merceri, from the inshore seas of the Philippines, New Guinea, and northeastern Australia.

All of the remaining atheriniform families are predominantly freshwater and are wholly restricted to Australia and the Indo-Pacific region, except for the Bedotiidae from the freshwaters of Madagascar. Rainbowfishes of the family Melanotaeniidae are abundant in New Guinea at elevations below 5,249 ft (1,600 m) as well as on numerous islands to the west of New Guinea. Additionally, they are found in Australia, mostly in river drainages in the northern and eastern regions of the continent. Pseudomugilids, from New Guinea, Australia, and Indonesia, and telmatherinids, from Sulawesi and Indonesia, can be found in fresh, brackish, and marine waters. Likewise, phallostethids occur in freshwaters and estuaries of the Southeast Asian mainland, the Philippines, and Sulawesi.

Habitat

Atheriniform habitats are as diverse as the fishes themselves. From the crashing surf zone of a Pacific island, where one might observe the silvery flashes of a school of Iso, to the still depths of a rainforest pool in New Guinea, where shoaling rainbowfishes dominate, atheriniforms have adapted to a range of aquatic conditions. Marine silversides can be found in almost all nonpolar, shallow marine habitats, including reefs, estuaries, and lagoons, and in the surf along beaches. Only a few species live in the open water. Freshwater atheriniforms occur in a variety of temperate and tropical lakes and streams, including spring-fed desert waterholes in Australia and mountain lakes in Patagonia.

Behavior

Atheriniforms are gregarious fishes that form schools of various sizes. Some marine silversides aggregate into enormous schools—numbering in the thousands—which cruise just below the surface, continually feeding on plankton. For instance, Atherinomorus capricornensis has been observed forming schools more than 328 ft (100 m) long and 65.6 ft (20 m) wide. At night silversides are attracted to bright lights and are caught easily by fishermen for use as bait. Some of the most interesting types of behavior found in atheriniforms, however, relate to reproduction.

Feeding ecology and diet

In general, atheriniforms are omnivorous, sometimes feeding on algae but depending more heavily on the most abundant forms of invertebrate protein in their respective habitats. For marine species, this means a heavy reliance on minute crustaceans and other forms of zooplankton. Fish larvae also are eaten by some species. In freshwaters, terrestrial insects often represent a significant portion of the diet. This is certainly true for the melanotaeniid rainbowfishes, which have a special preference for ants. In addition, freshwater atheriniforms feed on aquatic insects, zooplankton, and algae. Atheriniforms themselves are preyed upon by birds, mammals, and larger fishes, among other organisms. Marine silversides, in particular, which often aggregate in large schools, are sought after by larger fishes of commercial importance.

Reproductive biology

Peculiar reproductive repertoires are numerous within the atheriniformes. Large eggs with adhesive filaments are characteristic of the group; the filaments are used to anchor the eggs to aquatic plants or other forms of substrate. Among the rainbowfishes, spawning occurs day after day for an extended period, each day of which the female attaches a small number of thread-bearing eggs, fertilized externally by the male, to underwater plants. Eggs typically hatch in seven to 18 days. Atheriniform larvae generally are large (0.16–0.35 in; 4–9 mm) at hatching, and although they still possess a yolk sac, they have open mouths and can begin feeding immediately.

A truly exceptional reproductive strategy has evolved in grunion (two species of atherinids). Leuresthes tenuis and L. sardina both time their spawning to take advantage of tidal effects. Grunion spawn during periods of only a few hours on only six nights a month, when tides are highest around the times of the full and new moons (semilunar tides). The fishes ride in with large waves and are left stranded on the sand as the water recedes. Once on the beach, the female burrows into the sand with her tail to lay the eggs, and an accompanying male deposits his milt simultaneously. The fertilized eggs are left buried in the sand a few inches below the surface; they hatch in about two weeks, when semilunar high tides return to uncover them. Possible advantages for the eggs are decreased predation and increased oxygen levels and incubation temperature.

Male phallostethids, with their bizarre gripping structures (described earlier), ram females, and the two become locked together physically by the priapium during copulation. Frantic bursts of swimming are required for the pair to disengage. Further description of this behavior is provided in the species account of Neostethis bicornis.

In a lineage of Menidia, sexual reproduction has been for-gone entirely. The Menidia clarkhubbsi species complex from the Gulf of Mexico is made up of unisexual clonal lineages thought to be the result of hybridization events between M. beryllina and an as yet undetermined species, similar to M. peninsulae. The unisexuals produce eggs with a complete chromosomal complement that do not require fertilization but must still rely on sperm supplied by one of the bisexual species to stimulate embryo formation. Spawning itself is simple in Menidia. A single female—attended by several males— deposits eggs in aquatic vegetation, and the males leave milt; no courtship has been observed.

Conservation status

While no atheriniforms are listed by CITES, 79 species presently are included on the IUCN Red List. Of those, 28 species are listed as Data Deficient, 8 species are listed as Lower Risk/Near Threatened, and 31 species (most of which are rainbowfishes) are listed as Vulnerable. Five species are Endangered: Poblana letholepis and Poblana squamata from Mexico, Craterocephalus fluviatilis and Pseudomugil mellis from Australia, and Melanotaenia boesemani from New Guinea. Six species are considered Critically Endangered: Chilatherina sentaniensis from Irian Jaya, Glossolepis wanamensis and Kiunga ballochi from Papua New Guinea, Poblana alchichica from Mexico, Rheocles wrightae from Madagascar, and Scaturiginichthys vermeilipinnis from Australia. A single atheriniform, Rheocles sikorae from Madagascar, is believed to be Extinct.

A common trend holds true for the threatened atheriniforms: they are restricted to circumscribed freshwater habitats. Such habitats are particularly vulnerable. Water quality often is threatened by pollutants, including nutrients, which are the byproducts of such human activities as deforestation, mining, and waste disposal. Introduced fish species pose another serious problem; they can be detrimental to native fish populations both as resource competitors and as predators. In the United States—where freshwater atheriniforms are few— there are no atheriniforms listed as Endangered by the U. S. Fish and Wildlife Service. Only one species, Menidia extensa (the waccamaw silverside) from North Carolina, is listed as Threatened.

Significance to humans

Because of their small size, most atheriniforms are not sought as sources of food for humans, though there are exceptions to this rule. For instance, some large piscivorous Odontesthes species support thriving fisheries in lakes and reservoirs in Peru, Argentina, Chile, and southern Brazil. Marine silversides are indirectly important to commercial fisheries, in that they are an significant food source for many larger fish species that are valued as food fishes. When they are directly fished, small silversides typically are used as bait or converted into pet food.

In contrast, the freshwater rainbowfishes, owing to their extraordinary diversity of colors, are valued highly in the aquarium trade. At present, most of the rainbowfishes sold in pet stores are captive bred, but in the recent past some species were fished heavily to satisfy the demands of mostly European and American aquarists. Indeed, consider the case of the Boeseman's rainbow (see species account), which is considered Endangered. During the 1980s, when the fishery was unrestricted, tens of thousands of individuals were being removed from the wild each month for export.

Species accounts

Resources

Allen, Gerald R. Rainbowfishes in Nature and in the Aquarium. Melle, Germany: Tetra-Verlag, 1995.

Benton, M. J., ed. The Fossil Record 2. London: Chapman and Hall, 1993.

Berra, T. M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Breder, C. M., Jr., and D. E. Rosen. Modes of Reproduction in Fishes. Garden City, NY: Natural History Press, 1966.

Carpenter, K. E., and V. H. Niem, eds. FAO Species Identification Guide for Fishery Purposes. Vol. 4, The Living Marine Resources of the Western Central Pacific. Rome: FAO, 1999.

Echelle, A. A., and I. Kornfield, eds. Evolution of Fish Species Flocks. Orono: University of Maine at Orono Press, 1984.

Fischer, W., F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter, and V. H. Niem, eds. Guía FAO para Identificacíon de Especies para los Fines de la Pesca Pacifico Centro-Oriental. Vol. 2. Rome: FAO, 1995.

Hieronimus, Harro. All Rainbows and Related Families. Mörfelden-Walldorf, Germany: Verlag A.C.S., 2002.

Nelson, J. S. Fishes of the World. 3rd edition. New York: John Wiley and Sons, 1994.

Paxton, John R., and William N. Eschmeyer, eds. Encyclopedia of Fishes. 2nd edition. San Diego: Academic Press, 1998.

Riehl, Rudiger, and Hans A. Baensch. Aquarium Atlas, 2nd edition. Melle, Germany: Baensch, 1989.

Watson, W. "Atherinidae: Silversides." In The Early Stages of Fishes in the California Current Region, edited by H. G. Moser. California Cooperative Oceanic Fisheries Investigations (CalCOFI) Atlas no. 33. Lawrence, KS: Allen Press, 1996.

White, B. N., R. J. Lavenberg, and G. E. McGowan. "Atheriniformes: Development and Relationships." In Ontogeny and Systematics of Fishes, edited by H. G. Moser. Special Publication of the American Society of Ichthyology and Herpetology. Lawrence, KS: Allen Press, 1984.

Dyer, B. S., and B. Chernoff. "Phylogenetic Relationships Among Atheriniform Fishes (Teleostei: Atherinomorpha)." Zoological Journal of the Linnean Society 117, no. 1 (1996): 1–69.

Echelle, A. A., and A. F. Echelle. "Patterns of Abundance and Distribution Among Members of a Unisexual-Bisexual Complex of Fishes (Atherinidae: Menidia)." Copeia 1997, no. 2 (1997): 249–259.

Mok, E. Y. M., and A. D. Munro. "Some Anatomical and Behavioural Aspects of Reproduction in Members of an Unusual Teleost Family: The Phallostethidae." Journal of Natural History 31, no. 5 (1997): 739–778.

Parenti, L. R. "Relationships of Atherinomorph Fishes (Teleostei)." Bulletin of Marine Science 52, no. 1 (January 1993): 170–196. ——. "Phylogenetic Systematics and Biogeography of Phallostethid Fishes (Atherinomorpha, Phallostethidae) of Northwestern Borneo, with Description of a New Species." Copeia 1996, no. 3 (1996): 703–712.

Rosen, D. E. "The Relationships and Taxonomic Position of the Halfbeaks, Killifishes, Silversides, and Their Relatives." Bulletin of the American Museum of Natural History 127, no. 5(1964): 217–268.

Rosen, D. E., and L. R. Parenti. "Relationships of Oryzias, and the Groups of Atherinomorph Fishes." American Museum Novitates 2719 (November 1981): 1–25.

Saeed, B., W. Ivantsoff, and L. E. L. M. Crowley. "Systematic Relationships of Atheriniform Families Within Division I of the Series Atherinomorpha (Acanthopterygii) with Relevant Historical Perspectives." Journal of Ichthyology 34 (1994): 27–72.

Stiassny, Melanie L. J. "Notes on the Anatomy and Relationships of the Bedotiid Fishes of Madagascar, with a Taxonomic Revision of the Genus Rheocles (Atherinomorpha: Bedotiidae)." American Museum Novitates 2979 (August 1990): 1–33.

Stiassny, Melanie L. J. and Damaris M. Rodriguez. "Rheocles derhami, a New Species of Freshwater Rainbowfish (Atherinomorpha: Bedotiidae) from the Ambomboa River in Northeastern Madagascar." Ichthyological Exploration of Freshwaters 12, no. 2 (2001): 97–104.

Unmack, Peter J. "Biogeography of Australian Freshwater Fishes." Journal of Biogeography 28 (2001): 1053–1089.

[Article by: Robert Schelly, MA]

An order of actinopterygian fishes that includes the flyingfishes, needlefishes, killifishes, silversides, and their allies. Atheriniform fishes date from the Upper Cretaceous. Modern forms are grouped in 3 suborders, 16 families, about 170 genera, and probably 700–800 species. They chiefly inhabit fresh, brackish, and oceanic surface waters of the tropics and subtropics, but some enter the temperate zones, both in fresh water and the sea. They are circumtropical in distribution, abounding in fresh waters of Africa and the Americas and in all warm seas. None lives in deep oceanic waters. Atheriniformes are mostly small, although some needlefishes reach 5 ft (1.5 m) or more in length; most have a single dorsal fin of soft rays, but the silversides have a short anterior spinous dorsal; the pectoral fin is placed high on the side; the pelvic fin, if present, is abdominal, subabdominal, or thoracic and has six (occasionally seven) or fewer rays, one of which may be a spine; scales are usually cycloid, sometimes ctenoid, and rarely absent. The most familiar families include flyingfishes (see illustration) and halfbeaks (Exocoetidae), the former with stiffened, elongated rays on the paired fins that permit gliding in air; killifishes (Cyprinodontidae); live-bearers (Poeciliidae), among them guppies, swordtails, platyfishes, mollies, and mosquito fishes; and silversides (Atherinidae), that abound on marine beaches and reefs. Viviparity is more frequent and better understood in Atheriniformes than in any other order of bony fishes, occurring in no fewer than eight families. See also Actinopterygii; Osteichthyes.

California flyingfish (Cypselurus californicus). (After G. B. Goode, Fishery Industries of the U.S., 1884)

Silversides
Boeseman's rainbowfish, Melanotaenia boesemani, red variety
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Atheriniformes
Families
See text.

Atheriniformes, also known as the silversides, is an order of ray-finned fish that includes the Old World silversides and several less-familiar families, including the unusual Phallostethidae.

Description

Members of the order usually have two dorsal fins, the first with flexible spines, and an anal fin with one spine at the front. The lateral line is typically weak or absent.^[1] Atheriniform larvae share several characteristics; the gut is unusually short, there is a single row of melanophores along the back, and the fin rays do not become evident until some time after hatching.^[1]

Taxonomy

Classification of the atheriniforms is uncertain, with the best evidence for monophyly in the larval characteristics mentioned below.^[1]

Nelson, 2006, the family Melanotaeniidae includes the subfamilies Bedotiinae, Melanotaeniinae, Pseudomugilinae, and Telmatherininae, to demonstrate their monophyly.^[1] However, in a 2004 study, a different classification scheme classifies the families Bedotiidae, Melanotaeniidae, and Pseudomugilidae (also include Telmatherinine genera) in a suborder Melanotaenioidei.^[2] Thus, the number of families in Atheriniformes varies from author to author.

Classification under Nelson, 2006:^[1]

Order Atheriniformes

• Suborder Atherinopsoidei
  • Family Atherinopsidae (Neotropical silversides)
    • Subfamily Atherinopsinae
      • Tribe Atherinopsini
      • Tribe Sorgentinini
    • Subfamily Menidiinae
      • Tribe Menidiini
      • Tribe Membradini
• Suborder Atherinoidei
  • Infraorder Notocheiroida
    • Family Notocheiridae
  • Infraorder Atherinoida
    • Family Melanotaeniidae
      • Subfamily Bedotiinae
      • Subfamily Melanotaeniinae (rainbowfishes)
      • Subfamily Pseudomugilinae (blue eyes)
      • Subfamily Telmatherininae (sailfin silversides)
    • Family Atherionidae
    • Family Phallostethidae
      • Subfamily Dentatherininae
      • Subfamily Phallostethinae
        • Tribe Phallostethini
        • Tribe Gulaphallini
    • Family Atherinidae (silversides)
      • Subfamily Atherinomorinae
      • Subfamily Craterocephalinae
      • Subfamily Atherininae

References

1. ^ ^{a b c d e}
2. ^ Sparks, John S.; Smith, W. Leo (2004). "Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teleostei: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater" (PDF). Molecular Phylogenetics and Evolution 33: 719–734. 

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