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Catfish: (order
Siluriformes) are a very diverse group of bony fish. Named for their
prominent barbels, which resemble a cat's whiskers (though not
prominent in all members of this order), catfish range in size and
behavior from the heaviest, the Mekong giant catfish from Southeast
Asia and the longest, the wels catfish of Eurasia, to detritivores
(species that eat dead material on the bottom), and even to a tiny
parasitic species commonly called the candiru, Vandellia cirrhosa.
There are armour-plated types and also naked types, neither having
scales. Despite their common name, not all catfish have prominent
barbels; what defines a fish as being in the order Siluriformes are
in fact certain features of the skull and swimbladder. Catfish are
of considerable commercial importance; many of the larger species
are farmed or fished for food. Many of the smaller species,
particularly the genus Corydoras, are important in the aquarium
hobby.
The catfishes are a monophyletic group. This is supported by
molecular evidence.
Catfish belong to a superorder called the Ostariophysi, which also
includes the Cypriniformes, Characiformes, Gonorynchiformes and
Gymnotiformes, a superorder characterized by the Weberian apparatus.
Some place Gymnotiformes as a sub-order of Siluriformes, however
this is not as widely accepted. Currently, the Siluriformes are said
to be the sister group to the Gymnotiformes, though this has been
debated due to more recent molecular evidence. As of 2007[update]
there are about 36 extant catfish families, and about 3,023 extant
species have been described. This makes the catfish order the second
or third most diverse vertebrate order; in fact, 1 out of every 20
vertebrate species is a catfish.
The taxonomy of catfishes is quickly changing. In a 2007 and 2008
paper, Horabagrus, Phreatobius, and Conorhynchos were not classified
under any current catfish families. There is disagreement on the
family status of certain groups; for example, Nelson (2006) lists
Auchenoglanididae and Heteropneustidae as separate families, while
the All Catfish Species Inventory (ACSI) includes them under other
families. Also, FishBase and the Integrated Taxonomic Information
System lists Parakysidae as a separate family, while this group is
included under Akysidae by both Nelson (2006) and ACSI. Many sources
do not list the recently revised family Anchariidae. The family
Horabagridae, including Horabagrus, Pseudeutropius, and Platytropius,
is also not shown by some authors but presented by others as a true
group. Thus, the actual number of families differs between authors.
The species count is in constant flux due to taxonomic work as well
as description of new species. On the other hand, our understanding
of catfishes should increase in the next few years due to work by
the ACSI.
The rate of description of new catfishes is at an all-time high.
Between 2003 and 2005, over 100 species have been named, a rate
three times faster than that of the past century. In June, 2005,
researchers named the newest family of catfish, Lacantuniidae, only
the third new family of fish distinguished in the last 70 years
(others being the coelacanth in 1938 and the megamouth shark in
1983). The new species in Lacantuniidae, Lacantunia enigmatica, was
found in the Lacantun river in the Mexican state of Chiapas.
According to morphological data, Diplomystidae is usually considered
to be the most primitive of catfishes and the sister group to the
remaining catfishes, grouped in a clade called Siluroidei. Recent
molecular evidence contrasts the prevailing hypothesis, where the
suborder Loricarioidei are the sister group to all catfishes,
including Diplomystidae (Diplomystoidei) and Siluroidei; though they
were not able to reject the past hypothesis, the new hypothesis is
not unsupported. Siluroidei was found to be monophyletic without
Loricarioid families or Diplomystidae with molecular evidence;
morphological evidence is unknown that supports Siluroidei without
Loricarioidea.
Below is a list of family relationships by different authors.
Lacantuniidae is included in the Sullivan scheme based on recent
evidence that places it sister to Claroteidae.
Distribution and habitat
Extant catfish species live in inland or coastal waters of every
continent except Antarctica. Catfish have inhabited all continents
at one time or another. Catfish are most diverse in tropical South
America, Africa, and Asia. More than half of all catfish species
live in the Americas. They are the only ostariophysans that have
entered freshwater habitats in Madagascar, Australia, and New
Guinea.
They are found primarily in freshwater environments of all kinds,
though most inhabit shallow, running water habitats. Representatives
of at least eight families are hypogean (live underground) with
three families that are also troglobitic (inhabiting caves). Thus,
catfishes are some of the most successful cave colonizers among
fishes. One such species is Phreatobius cisternarum, known to live
underground in phreatic habitats. Numerous species from the families
Ariidae and Plotosidae, and a few species from among the
Aspredinidae and Bagridae, are also found in marine environments.
Physical characteristics
External anatomy
Most catfish are adapted for a benthic lifestyle. In general, they
are negatively buoyant, which means that they will usually sink
rather than float due to a reduced gas bladder and a heavy, bony
head. Catfish have a variety of body shapes, though most have a
cylindrical body with a flattened ventrum to allow for benthic
feeding.
A flattened head allows for digging through the substrate as well as
perhaps serving as a hydrofoil. Most have a mouth that can expand to
a large size and contains no incisiform teeth; catfish generally
feed through suction or gulping rather than biting and cutting prey.
However, some families, notably Loricariidae and Astroblepidae, have
a suckermouth that allows them to fasten themselves to objects in
fast-moving water. Catfish also have a maxilla reduced to a support
for barbels; this means that they are unable to protrude their
mouths as other fish such as carp.
Catfish may have up to four pairs of barbels: nasal, maxillary (on
each side of mouth), and two pairs of chin barbels, although pairs
of barbels may be absent, depending on the species. Because their
barbels are more important in detecting food, the eyes on catfish
are generally small. Like other ostariophysans, they are
characterized by the presence of a Weberian apparatus. Their
well-developed Weberian apparatus and reduced gas bladder allow for
improved hearing as well as sound production.
Catfish have no scales; their bodies are often naked. In some
species, the mucus-covered skin is used in cutaneous respiration,
where the fish breathes through its skin. In some catfish, the skin
is covered in bony plates called scutes; some form of body armor has
evolved a number of times within the order. In loricarioids and in
the Asian genus Sisor, the armor is primarily made up of one or more
rows of free dermal plates. Similar plates are found in large
specimens of Lithodoras. These plates may be supported by vertebral
processes, as in scoloplacids and in Sisor, but the processes never
fuse to the plates or form any external armor. By contrast, in the
subfamily Doumeinae (family Amphiliidae) and in hoplomyzontines (Aspredinidae),
the armor is formed solely by expanded vertebral processes that form
plates. Finally, the lateral armor of doradids, Sisor, and
hoplomyzontines consists of hypertrophied lateral line ossicles with
dorsal and ventral lamina.
All catfish, except members of Malapteruridae (electric catfish),
possess a strong, hollow, bonified leading spine-like ray on their
dorsal and pectoral fins. As a defense, these spines may be locked
into place so that they stick outwards, which can inflict severe
wounds. In several species catfish can use these fin rays to deliver
a stinging protein if the fish is irritated. This venom is produced
by glandular cells in the epidermal tissue covering the spines. In
members of the family Plotosidae, and of the genus Heteropneustes,
this protein is so strong it may hospitalize humans unfortunate
enough to receive a sting; in Plotosus lineatus, the stings may
result in death.
Juvenile catfish, like most fish, have relatively large heads, eyes
and posterior median fins in comparison to larger, more mature
individuals. These juveniles can be readily placed in their
families, particularly those with highly derived fin or body shapes;
in some cases identification of the genus is possible. As far as
known for most catfish, features that are often characteristic of
species such as mouth and fin positions, fin shapes, and barbel
lengths show little difference between juveniles and adults. For
many species, pigmentation pattern is also similar in juveniles and
adults. Thus, juvenile catfishes generally resemble and develop
smoothly into their adult form without distinct juvenile
specializations. Exceptions to this are the ariid catfishes, where
the young retain yolk sacs late into juvenile stages, and many
pimelodids, which may have elongated barbels and fin filaments or
coloration patterns.
Sexual dimorphism is reported in about half of all families of
catfish. The modification of the anal fin into an intromittent organ
(in internal fertilizers) as well as accessory structures of the
reproductive apparatus (in both internal and external fertilizers)
have been described in species belonging to 11 different families.
Size
Catfish have one of the greatest range in size within a single order
of bony fish. Many catfish have a maximum length of under 12 cm.
Some of the smallest species of Aspredinidae and Trichomycteridae
reach sexual maturity at only 1 centimetre (0.39 in).
The wels catfish, Silurus glanis, is the only native catfish species
of Europe, besides the much smaller related Aristotle's catfish
found in Greece. Mythology and literature record wels catfish of
astounding proportions, yet to be proven scientifically. The average
size of the species is about 1.2–1.6 m (3.9–5.2 ft), and fish more
than 2 metres (6.6 ft) are very rare. The largest specimens on
record measure more than 2.5 metres (8.2 ft) in length and sometimes
exceeded 100 kilograms (220 lb).
The largest Ictalurus furcatus, caught in the Mississippi River on
May 22, 2005, weighed 124 pounds (56 kg). The largest flathead
catfish, Pylodictis olivaris, ever caught was in Independence,
Kansas, weighing 123 lb 9 oz (56.0 kg). However, these records pale
in comparison to a giant Mekong catfish caught in northern Thailand
in May 1, 2005 and reported to the press almost 2 months later that
weighed 293 kilograms (650 lb). This is the largest giant Mekong
catfish caught since Thai officials started keeping records in 1981.
The giant Mekong catfish are not well studied since they live in
developing countries and it is quite possible that they can grow
even larger.
Internal anatomy
In many catfish, the humeral process is a bony process extending
backward from the pectoral girdle immediately above the base of the
pectoral fin. It lies beneath the skin where its outline may be
determined by dissecting the skin or probing with a needle.
The retina of catfish are composed of single cones and large rods.
Many catfish have a tapetum lucidum which may help enhance photon
capture and increase low-light sensitivity. Double cones, though
present in most teleosts are absent from catfish.
The anatomical organization of the testis in catfish is variable
among the families of catfish, but the majority of them present
fringed testis: Ictaluridae, Claridae, Auchenipteridae, Doradidae,
Pimelodidae, and Pseudopimelodidae. In the testes of some species of
Siluriformes, organs and structures such as a spermatogenic cranial
region and a secretory caudal region are observed, in addition to
the presence of seminal vesicles in the caudal region. The total
number of fringes and their length are different in the caudal and
cranial portions between species. Fringes of the caudal region may
present tubules, in which the lumen is filled by secretion and
spermatozoa. Spermatocysts are formed from cytoplasmic extensions of
Sertoli cells; the release of spermatozoa is allowed by breaking of
the cyst walls.
The occurrence of seminal vesicles, in spite of their interspecific
variability in size, gross morphology and function, has not been
related to the mode of fertilization. They are typically paired,
multi-chambered, and connected with the sperm duct, and have been
reported to play a glandular and a storage function. Seminal vesicle
secretion may include steroids and steroid glucuronides, with
hormonal and pheromonal functions, but it appears to be primarily
constituted of mucoproteins, acid mucopolysaccharides, and
phospolipids.
Fish ovaries may be of two types: gymnovarian or cystovarian. In the
first type, the oocytes are released directly into the coelomic
cavity and then eliminated. In the second type, the oocytes are
conveyed to the exterior through the oviduct. Many catfish are
cystovarian in type, including Pseudoplatystoma corruscans, P.
fasciatum, Lophiosilurus alexandri, and Loricaria lentiginosa.
Catfish as food
Catfish have been widely caught and farmed for food for hundreds of
years in Africa, Asia, Europe, and North America. Judgments as to
the quality and flavor vary, with some food critics considering
catfish as being excellent food, others dismiss them as watery and
lacking in flavour. In Central Europe, catfish were often viewed as
a delicacy to be enjoyed on feast days and holidays. Migrants from
Europe and Africa to the United States brought along this tradition,
and in the southern United States catfish is an extremely popular
food. The most commonly eaten species in the United States are the
channel catfish and blue catfish, both of which are common in the
wild and increasingly widely farmed. Catfish is eaten in a variety
of ways; in Europe it is often cooked in similar ways to carp, but
in the United States it is typically crumbed with cornmeal and
fried. In Indonesia catfish is a very popular food. They are usually
served grilled in street stalls called warung and eaten with
vegetables, the dish is called Pecel Lele (Lele is the Indonesian
word for catfish). In Malaysia catfish is called "Ikan Keli" ikan is
referred to as fish, ikan keli is also usually fried added with
spices according to preferences and is often eaten with steamed
rice. The iridescent shark is a common food fish in parts of
Asia. Vietnamese catfish cannot be legally marketed
as catfish in the US, and is subsequently referred to as swai.
Catfish is high in Vitamin D. Farm-raised catfish contains low
levels of omega-3 fatty acids and a much higher proportion of
omega-6 fatty acids.
As catfish lack scales, they are judged to not be kosher and cannot
be eaten by observant Jews.
Aquaculture
Main article: Farm-Raised Catfish
Catfish are easy to farm in warm climates, leading to inexpensive
and safe food at local grocers. Ictalurids are cultivated in North
America (especially in the Deep South, with Mississippi being the
largest domestic catfish producer). Channel catfish (Ictalurus
punctatus) supports a $450 million/yr aquaculture industry. In
Central Louisiana, Morgan W. Walker, Jr., an Alexandria businessman,
in 1970 converted a 1,100-acre cattle ranch into catfish ponds to
raise fish on a mass scale for sale and consumption.
Catfish raised in inland tanks or channels are considered safe for
the environment, since their waste and disease should be contained
and not spread to the wild.
In Asia, many catfish species are important as food. Several walking
catfish (Clariidae) and shark catfish (Pangasiidae) species are
heavily cultured in Africa and Asia. Exports of one particular shark
catfish species from Vietnam, Pangasius bocourti, has met with
pressures from the U.S. catfish industry. In 2003, The United States
Congress passed a law preventing the imported fish from being
labeled as catfish. As a result, the Vietnamese exporters of this
fish now label their products sold in the U.S. as "basa fish."
Trader Joe's has labeled frozen fillets of Vietnamese Pangasius
hypothalmus as "striper."
There is a large and growing ornamental fish trade, with hundreds of
species of catfish, such as Corydoras and armored suckermouth
catfish (often called plecos), being a popular component of many
aquaria. Other catfish commonly found in the aquarium trade are
banjo catfish, talking catfish, and long-whiskered catfish.
Catfish as invasive species
Walking catfish is an invasive species in Florida.Representatives of
the genus Ictalurus have been introduced into European waters in the
hope of obtaining a sporting and food resource. However, the
European stock of American catfishes has not achieved the dimensions
of these fishes in their native waters, and have only increased the
ecological pressure on native European fauna. Walking catfish have
also been introduced in the freshwaters of Florida, with the
voracious catfish becoming a major alien pest there. Flathead
catfish, Pylodictis olivaris, is also a North American pest on
Atlantic slope drainages. Pterygoplichthys species, released by
aquarium fishkeepers, have also established feral populations in
many warm waters around the world.
Source: Wikipedia.org, Copyright (c) 2009.
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