Loricariidae is the largest
family of
catfish
(Order Siluriformes), with almost 700 species and new species being
described each year.
Loricariids originate from fresh water habitats of Costa Rica
, Panama
, and
tropical and subtropical South
America. These fish are noted for the bony plates
covering their bodies and their
suckermouths. Several
genera are sold as "
plecos",
notably the suckermouth catfish,
Hypostomus plecostomus, and are
popular as
aquarium fish.
Common names
Members of the family Loricariidae are commonly referred to as
suckermouth armoured catfishes,
armoured catfish, 'plecos'
or simply 'plecs'; a shortened form of the species name
plecostomus.
These names are used practically interchangeably when referring to
the Loricariidae. The name "Plecostomus" and its shortened forms
have become synonymous with the Loricariidae in general, since
Plecostomus plecostomus (now called
Hypostomus
plecostomus) was one of the first species imported into the
fishkeeping hobby. This can cause some confusion as some unrelated
fish may also be called plecostomus, such as the "Borneo
Plecostomus", which are actually
balitorid fishes.
In their native range, these fish are known as
cascudos or
acarís.
L-numbers
Some types of loricariids are often referred to by their '
L-number'; this has been become common since
imports of loricariid catfish from South America often included
specimens that had not been
taxonomically described. Currently
L-numbers are used not only by fishkeeping enthusiasts but by
biologists since they represent a useful stopgap until a new
species of fish is given a full taxonomic name. It should be noted
that in some cases two different L-numbered catfish have turned out
to be different populations of the same species, while in other
cases multiple (but superficially similar) species have all been
traded under a single L-number.
Taxonomy and evolution
Because of their highly specialized morphology, loricariids have
been recognized as a
monophyletic
assemblage in even the earliest classifications of the
Siluriformes, meaning that it consists of a natural grouping with a
common ancestor and all of its descendents. Loricariidae is one of
seven families in the superfamily
Loricarioidea, along with
Amphiliidae,
Trichomycteridae,
Nematogenyidae,
Callichthyidae,
Scoloplacidae, and
Astroblepidae. Some of these families also
exhibit suckermouths or armor, although never together as in
Loricariids.
This is the largest
catfish family,
including about 684 species in around 92 genera, with new species
being described each year. However, this family is in flux and
revisions are likely. For example, the subfamily Ancistrinae is
accepted in as late as the 2006 edition of Nelson's
Fishes of the World; it later becomes
grouped as a tribe because of its recognition as a
sister group to the Pterygoplichthyini. Under
Ambruster, six subfamilies are recognized:
Delturinae,
Hypoptopomatinae,
Hypostominae,
Lithogeneinae,
Loricariinae, and
Neoplecostominae.
Monophyly for the family is strongly supported, except, possibly,
the inclusion of
Lithogenes.
Lithogenes is the only genus within the subfamily
Lithogeneinae. This genus and subfamily, the most
basal group in Loricariidae, is the
sister group to the rest of the family.
Neoplecostominae is the most basal group among the loricariids with
the exception of Lithogeneinae. However, the genera of
Neoplecostominae do not appear to form a
monophyletic assemblage. The two subfamilies
Loricariinae and Hypoptopomatinae appear to be generally regarded
as monophyletic. However, the monophyly and composition of the
other subfamilies are currently being examined and will likely be
altered substantially in the future. Hypostominae is the largest
subfamily of Loricariidae. It is made up of five
tribe. Four of the five tribes,
Corymbophanini,
Hypostomini,
Pterygoplichthyini, and
Rhinelepini, include about 24 genera. The fifth
and largest tribe,
Ancistrini (formerly
recognized as its own subfamily), includes 30 genera.
Loricariid
fossils are extremely rare. The
fossil record of Loricariidae extends
back to the upper
Miocene. Within the
superfamily
Loricarioidea,
Loricariidae is the most
derived; in this
superfamily, there is a trend toward increasingly complex jaw
morphology, which may have allowed for the great diversification of
the Loricariidae, which have the most advanced jaws.
Distribution and habitat
The family Loricariidae is vastly distributed over both sides of
the
Andes; on the other hand, most species are
generally restricted to small geographic ranges.
Loricariids are found
in fresh water habitats of Costa Rica, Panama, and
South America. Species occur in
swift-flowing streams from the lowlands up to 3,000 metres in
elevation. They can also be found in a variety of other freshwater
environments. They can be found in torrential mountain rivers,
quiet brackish estuaries, black acidic waters, and even in
subterranean habitats.
Description and biology
This family has extremely variable color patterns and body shapes.
Loricariids are characterized by bony plates covering their body,
similar to the bony plates in
callichthyids (In
Latin,
lorica means
corselet). These fish
exhibit a
ventral
suckermouth with
papilla (small
projections) on the lips. When present, the
adipose fin usually has a spine at the forward
edge. These fish have, when they are present, a unique pair of
maxillary barbels. These fish have
relatively long intestines due to their usually
herbivorous or
detrivorous diets. The body is characteristically
depressed in this family.
Taste buds cover
almost the entire surface of the body and fin spines. The length
can range from in some
Otocinclus to over in
Panaque,
Acanthicus, and
Pterygoplichthys.
One of the most obvious characteristics of the loricariids is the
suckermouth. The modified mouth and lips
allow the fish to feed, breathe, and attach to the substrate
through suction. It was once believed that lips could not function
as a sucker while respiration continued as the inflowing water
would cause the system to fail; however, it has been demonstrated
that respiration and suction can function simultaneously. Inflowing
water passing under the sucker is limited to a thin stream
immediately behind each maxillary barbel; the
maxillae in loricariids support only small maxillary
barbels and are primarily used to mediate the lateral lip tissue in
which they are embedded, preventing failure of suction during
inspiration . To achieve suction, the fish pressed its lips against
the substrate and inflates its mouth, causing negative
pressure.
Also, unlike most other catfish, the
premaxillae are highly mobile, and the lower jaws
have evolved towards a medial position with the teeth pointed
rostroventrally; these are important evolutionary innovations. The
fish rotates its lower and upper jaws to scrape the substrate. The
lower jaws are most mobile.
Loricariid catfishes have evolved several modifications of the
digestive tract that function as accessory
respiratory organ or
hydrostatic organs. These complex structures
would have been independently evolved a number of times. This
includes an enlarged stomach in the Pterygoplichthyini,
Hypostomus, and
Lithoxus,
a U-shaped
diverticulum in Rhinelepini,
and a ring-like diverticulum in
Otocinclus. However, even loricariids with
an unmodified stomach have a slight ability to breathe air.
Considerable
sexual dimorphism
occurs in this family, most pronounced during the breeding season.
For example, in
Loricariichthys, the male has a large
expansion of its lower lip, which it uses to hold a clutch of eggs.
Ancistrus males have snouts with
fleshy tentacles. In loricariids,
odontodes
develop almost anywhere on the external surface of the body and
first appear soon after hatching; odontodes appear in a variety of
shapes and sizes and are often sexually dimorphic, being larger in
breeding males. In most
Ancistrini
species, sharp evertible cheek spines (elongated odontodes) are
often more developed in males and are used in intraspecific
displays and combat.
Unusually for
bony fish, many species have
a modified
iris called an
omega iris. The top part of the iris descends to
form a loop which can expand and contract called an iris operculum;
when light levels are high, the pupil reduces in diameter and the
loop expands to cover the center of the pupil giving rise to a
crescent shaped light transmitting portion.
This feature gets its name from its similarity to an upside-down
Greek letter omega
(
Ω). The origins of this structure are unknown,
but it has been suggested that breaking up the outline of the
highly visible eye aids
camouflage in
what are often highly mottled animals. Species in the tribe
Rhinelepini are an exception among
loricariids, having a normal, circular iris. The presence or
absence of the iris operculum can also be used for identification
of species in the subfamily
Loricariinae.
Genetics
As of 2000, only 56 loricariid species have been cytogenically
investigated. It has been shown that 2n = 54 is the basal
diploid number of
chromosomes this family. There is a wide
variation in the chromosome number in this fish group, ranging from
2n = 36 in the
Loricariinae,
Rineloricaria
latirostris, to 2n = 96 in a species of
Upsilodus
(
Hemipsilichthys). Most
members of the Ancistrini and Pterygoplichthyini have 52
chromosomes. Karyotypic evolution by means of
centric fusion and
centric fissions seems to be a common
feature among loricariids; this is demonstrated by a higher number
of biarmed chromosomes in species with lower diploid number and
many uniarmed chromosomes in species with higher diploid numbers.
Studies conducted with representatives of some genera of
Hypostominae showed that within thisgroup, the
diploid number ranges from 2n = 52 to 2n =
80. However, the supposed wide karyotypic diversity that the family
Loricariidae or the subfamily Hypostominaewould present is almost
exclusively restricted to the genus
Hypostomus, and the species from the other
genera had a conserved diploid number. It has been found in some
species that there is a ZZ/ZW
sex-determination system.
Ecology
The suckermouth exhibited by these catfish allow them to adhere to
objects in their habitats, even in fast-flowing waters. The mouth
and teeth also are adapted to feed on a variety of foods such as
algae,
invertebrates, and
detritus. Some species, notably the
Panaque, are known for
xylophagy, or the ability to digest
wood.
Most species of Loricariids are
nocturnal animals. Some species are
territorial, while others, such
as
Otocinclus, prefer to live in
groups.
Air-breathing is well known among many loricariids. The ability to
breathe air is dependent on the risk of
hypoxia faced by a species;
torrent-dwelling species tend to have no ability to breathe air,
while low-land, pool-dwelling species such as those of
Hypostomus have a great ability to breathe air.
Pterygoplichthys are known for being kept out of water and
sold alive in fish markets, surviving up to 30 hours out of
water. Loricariids are facultative air breathers; they will only
breathe air if under stress and will only use their gills in
situations when oxygen levels are high. The dry season is a likely
time for this; there would be little food in the stomach, which
would allow its use for air breathing.
Loricariids exhibit a wide range of reproductive strategies,
including cavity spawning, attachment of eggs on the underside of
rocks, and egg-carrying. Parental care is usually well-developed
and the male guards the eggs and sometimes the larvae. The eggs
hatch after between 4 and 20 days, depending on the species.
In the aquarium
Loricariids are popular
aquarium fish,
where they are often sold as "plecs", "plecos" or "plecostomus".
These fish are often purchased because of their
algae-eating habits, though this role may not be
carried out. Most species are in fact
detritivores. A great many species of
Loricariids are also sold for their ornamental qualities,
representing many body shapes and colors.
Most species of Loricariids are nocturnal and will shy away from
bright light, appreciating some sort of cover to hide under
throughout the day. As they often originate from habitats with
fast-moving water,
filtration
should be vigorous.
A number of species of Loricariids have been bred in
captivity.
References
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