Astyanax aeneus | |
---|---|
Female (upper) and male (lower) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Characiformes |
Family: | Characidae |
Genus: | Astyanax |
Species: | A. aeneus |
Binomial name | |
Astyanax aeneus (Günther, 1860) | |
Astyanax aeneus, the banded tetra, is a small species of fish native to southern Central America and northern South America. It can be found in a variety of environments, including lakes, rivers, ponds, and slightly brackish locales like lagoons. As well as a varied habitat, it has a varied omnivorous diet: algae, seeds, leaves, insects, and fish fry appear to be the most common.
The IUCN considers A. aeneus a species of least concern, given its widespread habitat and hardy nature. Various threats throughout its range appear to have little impact on overall survivability. Despite a comparatively-short reproductive period, individuals also demonstrate high fecundity, which assists in maintaining a stable population.
Astyanax aeneus has silver sides, a white belly, and a greenish-brown back. There is a black rhomboidal shape on the caudal peduncle that extends to the tips of the middle caudal rays, but the fins are mostly transparent otherwise. Occasionally, the dorsal and caudal fins will display some red or yellow coloration. Upon preservation in alcohol, a gray band develops from the humeral spot to the caudal blotch; the humeral spot itself is distinct in living and deceased specimens, and is sometimes rhomboid or P-shaped. [2] Depending on the individual, there may be the suggestion of a second spot behind the first on both sides, but this is often just an intensification of the lateral stripe located there, and is not a true second humeral spot. [3]
The snout is blunt, and the mouth opens forward (as opposed to being upturned). The eye is almost half the size of the head, and is usually wider than the snout is long. Body depth is intermediate, ranging from 34 to 39% SL in larger specimens. [4] Notable morphometric characteristics include 9–11 dorsal-fin rays, 22–31 anal-fin rays (modally 25), and 10–11 pectoral-fin rays. A. aeneus is equipped with gill rakers for feeding, and southern populations may have a higher number of rakers than northern. [5]
Astyanax aeneus demonstrates notable sexual dimorphism. Females are the larger sex, reaching 12 cm (4.7 in) standard length (SL), while males reach 7.5 cm (3.0 in) SL. [2] As well as this, there are serrations on the maxillary bones of some large males, which is a feature also seen in some congeners. [6] Furthermore, males are more common than females, with a ratio of 1.8:1 males:females. [7] Occasionally, nuptial tubercles (small fleshy extensions on the anal or pelvic fins of male specimens) may develop; these are sometimes bifid. [3]
Body weight and standard length are positively correlated with the relative fecundity of specimens; in other words, large individuals are more likely to be capable of reproduction. [7] Spawning appears to be year-round in most of its range, but can be seasonally restricted depending on the specific site. [2] No matter the case, peak reproductive activity appears to be during warm and wet periods. For instance, populations of A. aeneus in the Champotón river mate the most during the stretch from April to July, and if water quality is poor, they can respond by transferring energy from the liver to increase gamete production, allowing year-round spawning. [7]
Astyanax aeneus is considered a keystone nutrient recycler, partially because of its varied appetite, and this specifically applies to phosphorus, which can limit the health of a given ecosystem (especially in neotropical streams like the ones it inhabits). [8] Furthermore, it is considered a good bioindicator of trace metals in the ecosystems of the Yucatán Peninsula, because of how the metals accumulate in the body. [9]
Stress levels measured by certain physiological responses to poor water conditions also make A. aeneus a good indicator of water quality in environments affected by various factors. One example is the Champotón river in southwestern Mexico, which is poorly studied but is under pressure from natural phenomena (like hurricanes) and anthropogenic hazards (like agriculture). [10] Anthropogenic hazards also include pesticides; cholinesterase activity in A. aeneus could possibly be used as a biomarker of pesticide exposure, but field research is inconclusive despite notable laboratory results. [11]
When originally named, A. aeneus was designated Tetragonopterus aeneus by Albert Günther in 1860. [12] In 1921, Carl H. Eigenmann reassigned Tetragonopterus aeneus to the genus Astyanax , which is where it currently belongs, but as a subspecies of Astyanax fasciatus, labeled Astyanax fasciatus aeneus. This is now considered an obsolete designation, and A. aeneus is recognized as its own species within Astyanax. [3]
In 1990, various specimens of A. aeneus were designated a new species, Astyanax armandoi, but the morphological characteristics said to warrant differentiation were found to be in line with standard inter- and intraspecies variation of A. aeneus, so the name Astyanax armandoi is now considered a junior synonym. [13] Further synonyms include Tetragonopterus humilis and Tetragonopterus microphthalmus, both given by Günther in 1864. [3]
Given its widespread and hardy nature, various species were once grouped together with A. aeneus before being given proper species designation. As such, A. aeneus is regarded as a cryptic species - that is, more than one species currently considered synonymous. [3] It is at the center of a species complex bearing its name.
Within Astyanax, there are three subgenera - Astyanax stricto sensu , Poecilurichthys, and Zygogaster. [14] A. aeneus belongs to the first. [3]
The word "aeneus" means "bronze" or "brazen" in Greek, referencing the brownish back. The specific epithet "aeneus" is not uncommon in taxonomy; consider Anolis aeneus, the bronze anole, or Molothrus aeneus, the bronzed cowbird. The specific reason for the genus name Astyanax is unknown, but the origin is in Homer's Iliad. Astyanax was a warrior of Troy, and was the son of famed warrior Hector. One possible reason for the allusion is the large, armor-like or shield-like scales of type species A. argentatus, which is now known as A.mexicanus. [15]
Astyanax aeneus is a widespread species. In Central America, countries include Mexico, in the rivers Papaloapan and Colima, Panama, in the rivers Cocle del Norte and Tabasara, and Honduras, in the Choluteca river. South America n countries with populations of A. aeneus include El Salvador and Guatemala. [1] [2] While largely freshwater, A. aeneus demonstrates no preference for one specific habitat or another. It is found in fast-flowing rivers, stagnant swamps, sizable lakes, and even the occasional brackish lagoon. [1] Whatever the case, it tends to linger in the stretch between the middle of the water column and the substrate. [4]
Because of its variable environment, A. aeneus is an adaptable species. One example of this is that the lower lip can expand to increase the surface area of the interface between water and air as a part of aquatic surface respiration (ASR) in hypoxic environments. [16] (A specific morphological variation in response to an environmental stressor is referred to as an ecophenotype.) This specific adaptation once led to the mistaken designation of a new species, A. armandoi, which has since been synonymized with A. aeneus. [13]
Astyanax aeneus has also adapted to cave environments in a similar manner to its more well-known cousin, the blind Mexican cavefish ( Astyanax mexicanus ). Changes include "eye and pigmentation regression, as well as modifications in brain morphology, behaviors, heart regenerative capacity, metabolic processes, and craniofacial organization" (as described by geneticist William R. Jeffery). [17] There are at least two populations of A. aeneus that are stygobitic (living solely in underground water sources, like caves or aquifers), but far more of A. mexicanus (more than 30). [18]
Astyanax aeneus is a voracious omnivore. Its diet includes algae, seeds, leaves, fruit, plant husks, insects (both aquatic and terrestrial, as well as larvae), and fish smaller than it, including fry of any species. [2] In turn, A. aeneus is sometimes a food source for human populations in rural areas, and is also subject to infestation by gill parasites from the flatworm family Monogenea; species include Anacanthocotyle anacanthocotyle, Characithecium costaricensis, Diaphorocleidus kabatai, Palombitrema heteroancistrium, and Urocleidoides strombicirrus. [19] In fact, Diaphorocleidus kabatai was first described from the gills of A. aeneus. [20]
If other fish in the same environment are too large to be eaten, A. aeneus can live in sympatry with them; most examples are congeners. Closely related species Astyanax cocibolca lives syntopically with A. aeneus in Lake Nicaragua. [6] A. aeneus and Astyanax caballeroi both inhabit Lake Catemaco, Mexico. [21] (A. aeneus and A. caballeroi, while they are visually distinct and are considered separate species, have little phenotypic difference; early-stage research presents the possibility that the species are synonymous, just different morphs.) [22]
Reportedly, A. aeneus is among the various species of Astyanax available for purchase in the aquarium trade, though their presence appears to be sparse. [23] They seem to be acceptable additions to a community aquarium, though only alongside other species that can keep up with its ravenous appetite and rambunctious nature. [24] Their active nature is a part of why they may be appealing. [25] At least one hobbyist report exists of A. aeneus being part of the exhibits in the Shedd Aquarium. [26]
Astyanax aeneus is considered a species of least concern by the IUCN due to its wide range and generally adaptable nature. Though its range was once wider due to accepted synonymy of species that are now considered separate, its population levels remain high and stable without signs of an imminent decrease or catastrophe. [1] This may change, given its status as a cryptic species; [3] if more speciation is revealed through study, then the range of A. aeneus may shrink as different populations are renamed entirely. However, this is unlikely.
The Mexican tetra, also known as the blind cave fish, blind cave characin or the blind cave tetra, is a freshwater fish in the Characidae family of the order Characiformes. The type species of its genus, it is native to the Nearctic realm, originating in the lower Rio Grande, and the Neueces and Pecos Rivers in Texas, into the Central Plateau and eastern states of Mexico.
Characidae, the characids or characins, is a family of freshwater subtropical and tropical fish belonging to the order Characiformes. The name "characins" is an historical one, but scientists today tend to prefer "characids" to reflect their status as a, by and large, monophyletic group. To arrive there, this family has undergone much systematic and taxonomic change. Among those fishes remaining in the Characidae currently are the tetras, comprising the very similar genera Hemigrammus and Hyphessobrycon, as well as a few related forms, such as the cave and neon tetras. Fish of this family are important as food in several regions, and also constitute a large percentage of captive freshwater aquarium fish species.
Tetra is the common name of many small freshwater characiform fishes. Tetras come from Africa, Central America, and South America, belonging to the biological family Characidae and to its former subfamilies Alestidae and Lebiasinidae. The Characidae are distinguished from other fish by the presence of a small adipose fin between the dorsal and caudal fins. Many of these, such as the neon tetra, are brightly colored and easy to keep in captivity. Consequently, they are extremely popular for home aquaria.
Astyanax is a genus of freshwater fish in the family Characidae of the order Characiformes. Some of these fish, like many of their relatives, are kept as aquarium pets and known collectively as tetras. With around 150 described species and new ones being described yearly, this genus is among the largest of the entire order; Hyphessobrycon also has more than 145 species and which one is larger at any one time depends on whether more species have been recently described in one or the other. The blind and colorless cave tetra of Mexico is a famous member of the genus, but its taxonomic position is disputed: Some recognize it as part of the Mexican tetra and this is supported by phylogenetic evidence, but others recognize the cave form as a separate species, A. jordani.
Carlastyanax aurocaudatus is a small species of freshwater fish in the family Characidae native to the Río Cauca in Colombia. It is the only member of the monotypic genus Carlastyanax, which was named in 1972 specifically for the species by Jacques Géry. Upon description, it was named Astyanax aurocaudatus by Carl H. Eigenmann. There has been debate concerning whether or not the genus should be recognized, but C. aurocaudatus is currently considered a valid species.
Astyanax argentatus is a small freshwater fish native to northern Central America and southern North America. Given its native range, it is also known as the Texan tetra. Little has been published regarding the feeding habits or behavior of A. argentatus, but it is known to have the northernmost distribution of any member of the genus Astyanax.
The tailspot tetra is a freshwater fish that lives in the coastal river regions of upper South America. Both its common and scientific names reference the distinct spot of color present on the tail fin, which is one of its defining characteristics. It is a small fish, reaching 4.8 in at its longest. Despite its small size, it is an active swimmer, with a preference for fast-flowing waters.
Astyanax acatlanensis, sometimes called the Acatlán tetra, is a small species of fish from the rivers of Mexico. It is a relatively hardy species that is able to tolerate a variety of water conditions, but is only found in freshwater, never brackish or marine. It is known only from the Río Acatlán, which is its type locality, and the Río Jía, which is a small, unknown river in the Oaxaca region.
Astyanax altior, the Yucatán tetra, is a small species of freshwater fish endemic to the Yucatán Peninsula of Mexico. It largely inhabits the cenotes of the region, and can tolerate water of limited salinity, though it largely prefers freshwater. Its diet includes plant matter and invertebrates, and there may be an element of cannibalism involved.
Astyanax altiparanae, sometimes called the yellow-tail tetra or yellow-tail lambari, is a species of schooling freshwater fish widely distributed across the southern half of South America. It is an ecologically flexible species, able to adapt to various resource and space conditions, and its diet follows this pattern; it is considered opportunistic and omnivorous. Its widespread nature and unspecified ecology contribute to its status as a species of least concern on the IUCN Red List. It was originally described from the upper Paraná river basin, which is the origin of its specific epithet; "alto" means "higher" in Brazilian Portuguese, hence "alto Paraná".
Astyanax angustifrons, sometimes referred to as the Campeche tetra, is a small freshwater fish from the rivers of Central and South America. It has a healthy distribution across southern Mexico and northern Guatemala, and is relatively common within its native range. Details regarding its diet and behavior are sparse, but it lives in areas with plentiful riparian vegetation, and most other members of the genus are omnivorous. Its habitat includes places affected by pollution and human activity; nonetheless, it is not endangered.
Astyanax bacalarensis, sometimes referred to as the Bacalar tetra, is a small species of freshwater fish found in Central and South America. Its scientific and common names both refer to its type locality, Lake Bacalar in Mexico, and it further inhabits freshwater environments like cenotes, streams, and wetlands. Its widespread nature, paired with an omnivorous diet, make it a hardy species.
Astyanax baileyi is a small freshwater fish native to northern Guatemala. Based on several visual aspects, it was once considered a member of the genus Bramocharax, which is now obsolete, and has since been synonymized with Astyanax. As such, former members of Bramocharax are now a part of Astyanax, like Astyanax bransfordii and Astyanax caballeroi.
Astyanax belizianus is a small freshwater fish native to various regions of Central America. Little is known of its diet or specific environmental preferences, but it was first recorded in Belize. Modern ichthyology has expanded its range into Guatemala and Honduras, where it inhabits various rivers and lake tributaries. It is a silvery fish that may have a slight yellowish tint to its scales. The body is deep, especially in comparison to similar species from the same genus.
The twospot astyanax, also called the two-spot tetra, is a small species of freshwater fish native to South America. It is a middlingly common tetra in the aquarium industry, with hobbyist reports of its sale and presence, and it is also a well-studied member of the genus Astyanax in wild settings. Amateur aquarists report peaceful schooling behavior in captivity, though fish in wild schools may turn on one another if presented with the threat of a predatory species.
Astyanax bransfordii, sometimes called the longjaw tetra, is a small carnivorous species of fish endemic to a handful of lakes and slow-moving canals in Central America. Its range includes Lake Nicaragua and Lake Managua, which are two of the largest freshwater bodies in Central America; because it occurs only in the relevant areas of Costa Rica and Nicaragua, the area it actually inhabits is somewhat restricted. Its diet largely consists of various invertebrates and smaller fish. This is in contrast to various other species of Astyanax, which are more often omnivorous.
Astyanax brevimanus, sometimes referred to as the Quiché tetra, is a small species of freshwater fish native to various locales in Guatemala. Its native range is somewhat restricted, but it is a populous and adaptable species, so there is no risk of it going extinct anytime soon. It is unknown what A. brevimanus eats, or what specific habitats it prefers; current information is largely in the form of physical descriptions, general areas of occurrence, and hypotheses regarding relationships to congeners. Its silvery scales, indistinct humeral (shoulder) spot, and dark caudal-peduncle spot are features not unusual in species of Astyanax.
Astyanax caballeroi is a small species of freshwater fish endemic to a single lake system in Mexico. It has a longer snout and more slender body than most other species in the genus Astyanax, thought to be the result of predatory behavior; while A. caballeroi eats invertebrates and smaller fish, other Astyanax species are more broadly omnivorous, and have deeper bodies with shorter snouts. This difference in body shape once placed A. caballeroi, along with several other species of Astyanax, into the former genus Bramocharax.
Astyanax caucanus is a small species of freshwater fish only found in Colombia. While little research exists regarding its ecological habits, such as diet and mating practices, its environment preferences are known to include marshy lowlands, and it easily lives in sympatry with various other fish species in the Cauca and Magdalena river basins. It is not known to share a habitat with any other species of Astyanax, but has a noted phyletic relationship to a group of congeners including Astyanax filiferus, Astyanax stilbe, and Astyanax magdalenae.
Astyanax clavitaeniatus is a small species of freshwater fish native to various rivers in the Amazon basin. It is characterized by a club-shaped lateral stripe, which is where it gets its scientific name; "clava" means "club", and "taenia" means "stripe". It is a deep-bodied fish with a silvery base color, which is not uncommon for members of Astyanax. Its markings - including a humeral spot and two vertical brown bars - indicate that it is a part of a species complex centered around congener Astyanax bimaculatus.
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