Glandulocaudinae
Encyclopedia
Glandulocaudinae is a subfamily of tropical
characin
fish
from Central
and South America
. In all species of this subfamily, a gland on their caudal fin
is found almost exclusively in the males, which allows the release and pumping of pheromone
s; also, members of this subfamily have complex courtship
behaviors which lead to insemination
. The ecology and life history of these fish is complex yet little studied. Glandulocaudines are important as food fish for larger fish important for commercial and subsistence reasons.
divided among seven monophyletic
, morphologically differing tribe
s. The monophyly of the subfamily itself needs much further investigation. There are about 60 species
. However, there remain many undescribed
species.
n drainage
s. Along Pacific
drainages, they are distributed from Costa Rica
to Ecuador
, and along Atlantic
drainages, their range extends to northern Argentina
. These fishes are found in every South American country, including Trinidad
and excluding Chile
; they inhabit streams that are tributaries
to larger rivers such as the Amazon
, Orinoco, and Paraguay River
s in tropical
species, or coastal streams tributary to the Atlantic and Pacific Oceans and the Caribbean Sea
in the few subtropical
species.
The habitat
s of these fish vary. A few species are known from elevation
s as high as 500–600 metres (1600–2000 ft), and Lophiobrycon weitzmani is known as high as 900 m (3000 ft). Some species are confined to acidic black rainforest waters, and others are found in clearer, neutral to somewhat alkaline waters; a few species are even adapted to both kinds of waters. However, there are no brackish water
species.
(about 2 in), but some species can be even smaller, between 11 and 30 millimetres (.4–1 in). The reproductive adaptations of glandulocaudines is what sets this group apart from the other Characins. Males have a caudal
organ associated with gland
tissue
s. Synapomorphies
of this subfamily include insemination
, a posterior sperm
storage area in the testes, and an elongate sperm nucleus.
All males have some form of modified caudal gland used to release pheromone
s as part of courtship
. The structure of this gland depends on the specific tribe; the organ may consist of modified caudal fin ray
s; modified caudal fin scale
s, a derived hypural
fan, or modified caudal fin musculature
, or combinations of the above. Modified scales may act as bellows
in releasing chemicals into the water. A caudal fin ray pheromone pump, unique to tribe Glandulocaudini, consists of glandular tissue associated with modified scales and fin rays. The tribe Diapomini is the only tribe in which the caudal gland is equally developed in both the males and females.
Females of all glandulocaudine species are inseminated. The females produce fewer egg
s per unit body weight than externally fertilizing species; this is possibly because insemination increases the efficiency of fertilization, so fewer eggs are necessary. This insemination is preceded by courtship
in all species. After insemination, the female may retain the live sperm for many months in her ovaries
. This allows the eggs to be laid when environmental conditions are favorable. However, there is no evidence of an intromittent organ
, and the exact mechanism of insemination is unknown. Hooks on the anal fin
of males may play a role, although these are also found in characins that exhibit external fertilization
. It was originally believed that internal fertilization
occurs in glandulocaudines. However, the exact time of fertilization is unknown and no fertilized eggs are found internally; this suggests fertilization occurs when the eggs are being laid or even outside of the body.
Due to insemination, the sperm
of glandulocaudines has adapted. In many species, an elongate cytoplasmic collar binds the flagellum
to the elongate nucleus at some stage of spermiogenesis. In almost all species, the sperm cell bodies are elongate. In the tribe Diapomini, the genus Planaltina expresses only round sperm (like that of externally fertilizing characins) and the genera Diapoma and Acrobrycon only express slightly elongated sperm; this may indicate a possible plesiomorphy
. Some sperm have enlarged regions containing mitochondria, which may help in prolonging the life of the sperm while stored in the ovary. In some genera, sperm clumping and patterns of arrangement are observed in the sperm ducts and storage regions. In the tribes Xenobryconini (in the genera Tyttocharax, Scopaeocharax, and Xenurobrycon) and Glandulocaudini, there is a form of sperm packaging which would allow for a higher sperm density during transfer from the male to the female. These packets are called spermatozeugmata, and the sperm are packaged parallel to each other; this packaging is further increased by the elongation of the sperm cells. In Xenobryconini, each spermatozeugma is produced and is released fully formed in the spermatocysts, but in Glandulocaudini, the sperm is released from the spermatocysts and packaged elsewhere. The spermatozeugmata are situated in the posterior end of the testes, which serves as a storage area for sperm.
Many of the genera also have a gland situated in the gill
cavity called a "gill gland", a secondary sex characteristic
found in sexually mature
male glandulocaudines that is apparently suited to release chemical signals. No genus contains species that have glands and other species without glands. This gill gland is derived from anterior gill filaments of the first gill arch
. Gland size and degree of gill modification varies with species. Though the true function of the gill glands has yet to be determined, they are probably used to release chemical signals into the gill current.
There are many examples of sexual dimorphism
(differences in appearance between the genders). In Corynopoma riisei
, the males have extended finnage (giving it the common name "swordtailed characin") as well as paddle-like extensions of the operculum
. Many other species also have other secondary sex characteristics believed to be involved in courtship.
Many of these characteristics are also shared with the tribe Compsurini in Cheirodontinae. Though unrelated, this group contains inseminating species with caudal organs. However, the caudal organs and other similar characteristics are structured differently. They also share the elongate cytoplasmic collar binding the flagellum to the elongate nucleus at some stage of spermiogenesis, which was previously assumed to be exclusive to glandulocaudines. These fish also occasionally have gill glands.
s, glandulocaudines show a reaction to chemical signals in the water. Many ostariophysans have a fright reaction in response to an alarm substance. In Corynopoma riisei
, it has been shown that a sexually mature
male's presence actually inhibits the maturation of immature males. In C. riisei, the female is often situated parallel to and somewhat behind the male, which allows for chemical signals released from the male's gill glands to be carried directly to the female.
Glandulocaudines have complex courtship
behavior. In C. riisei, the male has paddle-shaped extensions of the operculum which can be extended perpendicular to its body and twitches and flutters due to movements of his body; the female follows and nips at these projections during courtship.
A croaking behavior is recorded in some species of Mimagoniates
. This behavior has a part in courtship as well. Courtship involves the male chasing and hovering near the female. As the male hovers, he will quickly swim to the surface and take a gulp of air and return, expelling the gas and making continuous, rhythmic pulses of croaking sounds, interrupted only by the male returning to the surface for more air. The fish also zigzag
s while hovering by swimming up and down, when the fish intends to resurface but does not. Croaking behavior may have evolved from a behavior called "nipping surface", a feeding behavior that occurs when the fish is searching for food; the fish often will gulp air when doing this. This gulping of air has no respiratory
significance.
trade. Herbert R. Axelrod
has discussed the care of a number of species, including Corynopoma riisei, Gephyrocharax caucanus, Mimagoniates microlepis
, M. lateralis
, M. inequalis
, Pseudocorynopoma doriae, and Tyttocharax madeirae. These species reach about 5–6 cm (about 2 in). However, T. madeirae reaches 2 cm (less than 1 in), while P. doriae reaches 8 cm (3 in). Like most tetra
s, they prefer to swim in schools
; some species may be nippy, and should be kept in groups to divide aggression. Many species are very active and will almost constantly swim, which translates to a larger aquarium. They have been bred in captivity.
These fish may not be as easily weaned onto dry food
s as other fish, and will appreciate live food
s. Some species appreciate cooler water than the average tropical fish
, so this should be kept in mind when maintaining some of these species. Also, many imported specimens, even if they seem healthy, may mysteriously waste away. Some species are delicate and are not easily collected or transported, or are rarely seen available.
. ITIS
does not list Characin
subfamilies as they believe subfamilies are likely to change.
Tribe Landonini
Tribe Glandulocaudini
Tribe Diapomini
Tribe Phenacobryconini
Tribe Hysteronotini
Tribe Corynopomini
Tribe Xenurobryconini
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
characin
Characidae
The Characidae, characids or characins are a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their status as a by and large monophyletic group at family...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
from Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. In all species of this subfamily, a gland on their caudal fin
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
is found almost exclusively in the males, which allows the release and pumping of pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s; also, members of this subfamily have complex courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
behaviors which lead to insemination
Insemination
Insemination is the deliberate introduction of sperm into the uterus of a mammal or the oviduct of an oviparous animal for the objective of impregnating a female for reproduction...
. The ecology and life history of these fish is complex yet little studied. Glandulocaudines are important as food fish for larger fish important for commercial and subsistence reasons.
Taxonomy
Glandulocaudinae consists of twenty generaGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
divided among seven monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
, morphologically differing tribe
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
s. The monophyly of the subfamily itself needs much further investigation. There are about 60 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. However, there remain many undescribed
Undescribed taxon
In taxonomy, an undescribed taxon is a taxon that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. Until such a description has been published, the taxon has no formal or...
species.
Distribution and habitat
Glandulocaudines occur in practically all major South AmericaSouth America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
n drainage
Drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
s. Along Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
drainages, they are distributed from Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
to Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
, and along Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
drainages, their range extends to northern Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. These fishes are found in every South American country, including Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
and excluding Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
; they inhabit streams that are tributaries
Tributary
A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...
to larger rivers such as the Amazon
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
, Orinoco, and Paraguay River
Paraguay River
The Paraguay River is a major river in south central South America, running through Brazil, Bolivia, Paraguay, and Argentina...
s in tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
species, or coastal streams tributary to the Atlantic and Pacific Oceans and the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
in the few subtropical
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
species.
The habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s of these fish vary. A few species are known from elevation
Elevation
The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....
s as high as 500–600 metres (1600–2000 ft), and Lophiobrycon weitzmani is known as high as 900 m (3000 ft). Some species are confined to acidic black rainforest waters, and others are found in clearer, neutral to somewhat alkaline waters; a few species are even adapted to both kinds of waters. However, there are no brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
species.
Characteristics
Glandulocaudines are small, less than 13 centimetres (5 in). Most are between about 5–6 cm SLFish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
(about 2 in), but some species can be even smaller, between 11 and 30 millimetres (.4–1 in). The reproductive adaptations of glandulocaudines is what sets this group apart from the other Characins. Males have a caudal
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
organ associated with gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
s. Synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of this subfamily include insemination
Insemination
Insemination is the deliberate introduction of sperm into the uterus of a mammal or the oviduct of an oviparous animal for the objective of impregnating a female for reproduction...
, a posterior sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
storage area in the testes, and an elongate sperm nucleus.
All males have some form of modified caudal gland used to release pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s as part of courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
. The structure of this gland depends on the specific tribe; the organ may consist of modified caudal fin ray
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
s; modified caudal fin scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s, a derived hypural
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
fan, or modified caudal fin musculature
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
, or combinations of the above. Modified scales may act as bellows
Bellows
A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...
in releasing chemicals into the water. A caudal fin ray pheromone pump, unique to tribe Glandulocaudini, consists of glandular tissue associated with modified scales and fin rays. The tribe Diapomini is the only tribe in which the caudal gland is equally developed in both the males and females.
Females of all glandulocaudine species are inseminated. The females produce fewer egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s per unit body weight than externally fertilizing species; this is possibly because insemination increases the efficiency of fertilization, so fewer eggs are necessary. This insemination is preceded by courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
in all species. After insemination, the female may retain the live sperm for many months in her ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
. This allows the eggs to be laid when environmental conditions are favorable. However, there is no evidence of an intromittent organ
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
, and the exact mechanism of insemination is unknown. Hooks on the anal fin
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
of males may play a role, although these are also found in characins that exhibit external fertilization
External fertilization
External fertilization is a form of fertilization in which a sperm cell is united with an egg cell external to the bodies of the reproducing individuals. In contrast, internal fertilization takes place inside the female after insemination through copulation....
. It was originally believed that internal fertilization
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...
occurs in glandulocaudines. However, the exact time of fertilization is unknown and no fertilized eggs are found internally; this suggests fertilization occurs when the eggs are being laid or even outside of the body.
Due to insemination, the sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
of glandulocaudines has adapted. In many species, an elongate cytoplasmic collar binds the flagellum
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
to the elongate nucleus at some stage of spermiogenesis. In almost all species, the sperm cell bodies are elongate. In the tribe Diapomini, the genus Planaltina expresses only round sperm (like that of externally fertilizing characins) and the genera Diapoma and Acrobrycon only express slightly elongated sperm; this may indicate a possible plesiomorphy
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
. Some sperm have enlarged regions containing mitochondria, which may help in prolonging the life of the sperm while stored in the ovary. In some genera, sperm clumping and patterns of arrangement are observed in the sperm ducts and storage regions. In the tribes Xenobryconini (in the genera Tyttocharax, Scopaeocharax, and Xenurobrycon) and Glandulocaudini, there is a form of sperm packaging which would allow for a higher sperm density during transfer from the male to the female. These packets are called spermatozeugmata, and the sperm are packaged parallel to each other; this packaging is further increased by the elongation of the sperm cells. In Xenobryconini, each spermatozeugma is produced and is released fully formed in the spermatocysts, but in Glandulocaudini, the sperm is released from the spermatocysts and packaged elsewhere. The spermatozeugmata are situated in the posterior end of the testes, which serves as a storage area for sperm.
Many of the genera also have a gland situated in the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
cavity called a "gill gland", a secondary sex characteristic
Secondary sex characteristic
Secondary sex characteristics are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship and aggressive...
found in sexually mature
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
male glandulocaudines that is apparently suited to release chemical signals. No genus contains species that have glands and other species without glands. This gill gland is derived from anterior gill filaments of the first gill arch
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
. Gland size and degree of gill modification varies with species. Though the true function of the gill glands has yet to be determined, they are probably used to release chemical signals into the gill current.
There are many examples of sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
(differences in appearance between the genders). In Corynopoma riisei
Corynopoma riisei
Corynopoma riisei, the Swordtail characin, is a species of characin found in Colombia, Trinidad and Tobago and Venezuela. It is also kept as an aquarium fish. This species is the only member of its genus....
, the males have extended finnage (giving it the common name "swordtailed characin") as well as paddle-like extensions of the operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
. Many other species also have other secondary sex characteristics believed to be involved in courtship.
Many of these characteristics are also shared with the tribe Compsurini in Cheirodontinae. Though unrelated, this group contains inseminating species with caudal organs. However, the caudal organs and other similar characteristics are structured differently. They also share the elongate cytoplasmic collar binding the flagellum to the elongate nucleus at some stage of spermiogenesis, which was previously assumed to be exclusive to glandulocaudines. These fish also occasionally have gill glands.
Courtship
Like other ostariophysanOstariophysi
Ostariophysi is the second-largest superorder of fish. Members of this superorder are called ostariophysians. 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 all major continents except Antarctica...
s, glandulocaudines show a reaction to chemical signals in the water. Many ostariophysans have a fright reaction in response to an alarm substance. In Corynopoma riisei
Corynopoma riisei
Corynopoma riisei, the Swordtail characin, is a species of characin found in Colombia, Trinidad and Tobago and Venezuela. It is also kept as an aquarium fish. This species is the only member of its genus....
, it has been shown that a sexually mature
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
male's presence actually inhibits the maturation of immature males. In C. riisei, the female is often situated parallel to and somewhat behind the male, which allows for chemical signals released from the male's gill glands to be carried directly to the female.
Glandulocaudines have complex courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
behavior. In C. riisei, the male has paddle-shaped extensions of the operculum which can be extended perpendicular to its body and twitches and flutters due to movements of his body; the female follows and nips at these projections during courtship.
A croaking behavior is recorded in some species of Mimagoniates
Mimagoniates
Mimagoniates is a genus of Stevardiinae, a subfamily of tropical characid fish from Central and South America. Commonly known as croaking tetras or chirping tetras because they can produce sounds, some of these fish were formerly included in Glandulocauda.They have a supplementary breathing organ...
. This behavior has a part in courtship as well. Courtship involves the male chasing and hovering near the female. As the male hovers, he will quickly swim to the surface and take a gulp of air and return, expelling the gas and making continuous, rhythmic pulses of croaking sounds, interrupted only by the male returning to the surface for more air. The fish also zigzag
Zigzag
A zigzag is a pattern made up of small corners at variable angles, though constant within the zigzag, tracing a path between two parallel lines; it can be described as both jagged and fairly regular....
s while hovering by swimming up and down, when the fish intends to resurface but does not. Croaking behavior may have evolved from a behavior called "nipping surface", a feeding behavior that occurs when the fish is searching for food; the fish often will gulp air when doing this. This gulping of air has no respiratory
Aquatic respiration
Aquatic respiration is the process whereby an aquatic animal obtains oxygen from water.-Fish:In most fish respiration takes place through gills. Lungfish, however, possess one or two lungs...
significance.
In the aquarium
Some species of Glandulocaudinae are important in the aquariumAquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
trade. Herbert R. Axelrod
Herbert R. Axelrod
Herbert Richard Axelrod is a tropical fish expert, publisher of pet books, and entrepreneur. In 2005 he was sentenced in U.S. court to 18 months in prison for tax fraud.-Early life:...
has discussed the care of a number of species, including Corynopoma riisei, Gephyrocharax caucanus, Mimagoniates microlepis
Mimagoniates microlepis
Mimagoniates microlepis, also known as the Blue Tetra , the Croaking Tetra , the Small-Scaled Tetra, is a species of tetra in the genus Mimagoniates...
, M. lateralis
Mimagoniates lateralis
Mimagoniates lateralis is a species of tetra in the genus Mimagoniates. Its common names includeCroaking Tetra ....
, M. inequalis
Mimagoniates lateralis
Mimagoniates lateralis is a species of tetra in the genus Mimagoniates. Its common names includeCroaking Tetra ....
, Pseudocorynopoma doriae, and Tyttocharax madeirae. These species reach about 5–6 cm (about 2 in). However, T. madeirae reaches 2 cm (less than 1 in), while P. doriae reaches 8 cm (3 in). Like most tetra
Tetra
thumb|right|250px|Pristella tetra — [[Pristella maxillaris]].thumb|right|250px|Golden Pristella tetra, a [[morph |morph]] of [[Pristella maxillaris]].thumb|right|250px|[[Silvertip tetra]] — Hasemania nana....
s, they prefer to swim in schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
; some species may be nippy, and should be kept in groups to divide aggression. Many species are very active and will almost constantly swim, which translates to a larger aquarium. They have been bred in captivity.
These fish may not be as easily weaned onto dry food
Fish food
Aquarium fish feed is plant or animal material intended for consumption by pet fish kept in aquariums or ponds. Fish foods normally contain macro nutrients, trace elements and vitamins necessary to keep captive fish in good health. Approximately 80% of fishkeeping hobbyists feed their fish...
s as other fish, and will appreciate live food
Live food
Live food is living food for carnivorous or omnivorous animals kept in captivity; in other words, small animals such as insects or mice fed to larger carnivorous or omnivorous species kept in either in a zoo or as pet....
s. Some species appreciate cooler water than the average tropical fish
Tropical fish
Tropical fish include fish found in tropical environments around the world, including both freshwater and salt water species.Tropical fish are popular as aquarium fish, due to their often bright coloration...
, so this should be kept in mind when maintaining some of these species. Also, many imported specimens, even if they seem healthy, may mysteriously waste away. Some species are delicate and are not easily collected or transported, or are rarely seen available.
Species
Species list is according to FishBaseFishBase
FishBase is a comprehensive database of information about fish species . It is the largest and most extensively accessed online database on adult finfish on the web...
. ITIS
Itis
Itis may refer to* Integrated Taxonomic Information System, a partnership designed to provide consistent and reliable information on the taxonomy of biological species...
does not list Characin
Characidae
The Characidae, characids or characins are a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their status as a by and large monophyletic group at family...
subfamilies as they believe subfamilies are likely to change.
Tribe Landonini
- Landonia
- Landonia latidensLandonia latidensLandonia latidens is a species of characin endemic to Ecuador where it occurs in the Vinces River. It is the only species in its genus....
Eigenmann & Henn, 1914
- Landonia latidens
Tribe Glandulocaudini
- GlandulocaudaGlandulocaudaGlandulocauda is a genus of characins endemic to Brazil. There are currently two described species in this genus.-Species:* Glandulocauda caerulea Menezes & Weitzman, 2009* Glandulocauda melanopleura...
- Glandulocauda melanogenys Eigenmann, 1911
- Glandulocauda melanopleura Eigenmann, 1911
- Lophiobrycon
- Lophiobrycon weitzmaniLophiobrycon weitzmaniLophiobrycon weitzmani is a species of characin endemic to Brazil where it is found in the upper Paraná River basin. It is the only member of its genus....
Castro, Ribeira, Benine & Melo, 2003
- Lophiobrycon weitzmani
- MimagoniatesMimagoniatesMimagoniates is a genus of Stevardiinae, a subfamily of tropical characid fish from Central and South America. Commonly known as croaking tetras or chirping tetras because they can produce sounds, some of these fish were formerly included in Glandulocauda.They have a supplementary breathing organ...
- Mimagoniates barberi Regan, 1907
- Mimagoniates inequalisMimagoniates inequalisMimagoniates inequalis, known as the Croaking Tetra , is a species of tetra in the genus Mimagoniates. It was previously classified as Glandulocauda inequalis...
(Eigenmann, 1911) - Mimagoniates lateralisMimagoniates lateralisMimagoniates lateralis is a species of tetra in the genus Mimagoniates. Its common names includeCroaking Tetra ....
(Nichols, 1913) - Mimagoniates microlepisMimagoniates microlepisMimagoniates microlepis, also known as the Blue Tetra , the Croaking Tetra , the Small-Scaled Tetra, is a species of tetra in the genus Mimagoniates...
(Steindachner, 1876) - Mimagoniates rheocharis Menezes & Weitzman, 1990
- Mimagoniates sylvicola Menezes & Weitzman, 1990
Tribe Diapomini
- AcrobryconAcrobryconAcrobrycon is a genus of characin found in tropical South America. There are currently two described species in this genus.-Species:* Acrobrycon ipanquianus * Acrobrycon tarijae Fowler, 1940...
- Acrobrycon ipanquianus (Cope, 1877)
- Acrobrycon tarijae Fowler, 1940
- DiapomaDiapomaDiapoma is a genus of characins from tropical South America. There are currently four described species in this genus.-Species:* Diapoma pyrrhopteryx Menezes & Weitzman, 2011* Diapoma speculiferum Cope, 1894* Diapoma terofali...
- Diapoma speculiferum Cope, 1894
- Diapoma terofoli (Géry, 1964)
- PlanaltinaPlanaltina (genus)Planaltina is a genus of characins endemic to Brazil. There are currently three described species in this genus.-Species:* Planaltina britskii Menezes, Weitzman & J. R. Burns, 2003* Planaltina glandipedis Menezes, Weitzman & J. R. Burns, 2003...
- Planaltina britskii Menezes, Weitzman & Burns, 2003
- Planaltina glandipedis Menezes, Weitzman & Burns, 2003
- Planaltina myersi Böhlke, 1954
Tribe Phenacobryconini
- Phenacobrycon
- Phenacobrycon henniPhenacobrycon henniPhenacobrycon henni is a species of characin endemic to Ecuador where it is found in the Vinces River basin. It is the only member of its genus....
(Eigenmann, 1914)
- Phenacobrycon henni
Tribe Hysteronotini
- Hysteronotus
- Hysteronotus megalostomusHysteronotus megalostomusHysteronotus megalostomus is a species of characin endemic to Brazil where it is found in the upper São Francisco River basin. It is the only member of its genus....
Eigenmann, 1922
- Hysteronotus megalostomus
- Pseudocorynopoma
- Pseudocorynopoma doriai Perugia, 1891
- Pseudocorynopoma heterandria Eigenmann, 1914
Tribe Corynopomini
- Corynopoma
- Corynopoma riiseiCorynopoma riiseiCorynopoma riisei, the Swordtail characin, is a species of characin found in Colombia, Trinidad and Tobago and Venezuela. It is also kept as an aquarium fish. This species is the only member of its genus....
Gill, 1858
- Corynopoma riisei
- GephyrocharaxGephyrocharaxGephyrocharax is a genus of characins found in Central and South America. There are currently 12 described species in this genus.-Species:* Gephyrocharax atracaudatus * Gephyrocharax caucanus C. H. Eigenmann, 1912...
- Gephyrocharax atracaudatus (Meek & Hildebrand, 1912)
- Gephyrocharax caucanus Eigenmann, 1912
- Gephyrocharax chaparae Fowler, 1940
- Gephyrocharax chocoensis Eigenmann, 1912
- Gephyrocharax intermedius Meek & Hildebrand, 1916
- Gephyrocharax major Myers, 1929
- Gephyrocharax martae Dahl, 1943
- Gephyrocharax melanocheir Eigenmann, 1912
- Gephyrocharax sinuensis Dahl, 1964
- Gephyrocharax valencia Eigenmann, 1920
- Gephyrocharax venezuelae Schultz, 1944
- Gephyrocharax whaleri Hildebrand, 1938
- Pterobrycon
- Pterobrycon landoni Eigenmann, 1913
- Pterobrycon myrnae Bussing, 1974
Tribe Xenurobryconini
- ArgopleuraArgopleuraArgopleura is a genus of characin endemic to Colombia. There are currently four described species in this genus.-Species:* Argopleura chocoensis * Argopleura conventus...
- Argopleura chocoensis (Eigenmann, 1913)
- Argopleura conventus (Eigenmann, 1913)
- Argopleura diquensis (Eigenmann, 1913)
- Argopleura magdalenensis (Eigenmann, 1913
- ChrysobryconChrysobryconChrysobrycon is a genus of characins endemic to Peru. There are currently two species in this genus.-Species:* Chrysobrycon hesperus * Chrysobrycon myersi...
- Chrysobrycon hesperus (Böhlke, 1958)
- Chrysobrycon myersi (Weitzman & Thomerson, 1970)
- Iotabrycon
- Iotabrycon praecoxIotabrycon praecoxIotabrycon praecox is a species of characin endemic to Ecuador where it is found in the Vinces River basin. It is the only member of its genus....
Roberts, 1973
- Iotabrycon praecox
- Ptychocharax
- Ptychocharax rhyacophila Weitzman, Fink, Machado-Allison & Royero L., 1994
- Scopaeocharax
- Scopaeocharax atopodus (Böhlke, 1958)
- Scopaeocharax rhinodus (Böhlke, 1958)
- Tyttocharax
- Tyttocharax cochui (Ladiges, 1950)
- Tyttocharax madeirae Fowler, 1913
- Tyttocharax tambopatensis Weitzman & Ortega, 1995
- Xenurobrycon
- Xenurobrycon coracoralinae Moreira, 2005
- Xenurobrycon heterodon Weitzman & Fink, 1985
- Xenurobrycon macropus Myers & Miranda-Ribeiro, 1945
- Xenurobrycon polyancistrus Weitzman, 1987
- Xenurobrycon pteropus Weitzman & Fink, 1985