Callichthyids are armored catfishes living in South America, and are found in most of its freshwater environments. Some species, particularly of the genus Corydoras, are very well known and are appreciated as aquarium pets worldwide. Most callichthyids are bottom dwellers and eat mainly aquatic invertebrates, especially microcrustaceans and insects, as well as lots of detritus. Some species are so common in some parts of South America, that they are fished commercially as food fishes. They are usually cooked in their bony armor and they are really very tasteful.
This family has approximately 161 species grouped in eight genera (about 7.1% of all Siluriformes). Of these species, approximately 130 belong to Corydoras, the largest siluriform genus. A complete catalogue of species, a list of original literature and a key to genera of callichthyids are available.
The callichthyids inhabit a variety of different habitats in the Neotropical region, from small, swift, oxygen-rich creeks to big rivers and flooded areas, including swampy and muddy habitats where oxygen might be virtually absent. To survive in these habitats, callichthyids perform air-breathing. The air is collected at the water surface and swallowed, since their "accessory respiratory organ" is the intestine, and is eventually expelled through the anus. In this family, however, the air swallowed plays a more important role in the maintenance of the hydrostatic balance than in respiration itself, contributing with about 75% of the necessary air for neutral buoyancy (Gee, 1976; Gee & Graham, 1978). Additionally, unlike the catfishes in the families Loricariidae and Trichomycteridae that practice aerial respiration only in case of hypoxia, the Callichthyidae breathe air continuously under all water conditions.
Also very interesting are the reproductive habits of the callichthyids. Aspidoras, Corydoras and Brochis share with most siluroids the condition of substrate brooding. Eggs are laid on substrates like rocks, logs, or leaves. Callichthys, Megalechis, Lepthoplosternum, Hoplosternum and Dianema, on the other hand, have the interesting behavior of building floating nests composed of foam and vegetal debris. Spawning and caring for the eggs and larvae takes place in these nests (see Burgess, 1987, 1989 for some photos).
The fishes of the family Callichthyidae are distinguished and easilyrecognized by having the body almost completely protected by a bony armorcomposed of two longitudinal series of dermal plates.
Fishes in this family vary from small to medium-size. Some species ofCorydoras reach no more than 20 mm, whereas Hoplosternum littorale,the largest species, grows up to about 160 mm of standard length.
The family Callichthyidae presents many derived features, some of themost interesting are: sensory canal of the lateral line reduced to 1-6plates; preopercle sensory canal not connected to the preopercular ramusin the pterotic-supracleithrum; infraorbital bones expanded as plates;first infraorbital bearing an inner laminar expansion, forming the floorof the orbital cavity; second infraorbital with an inner laminar expansion,forming the posterior wall of the orbit; second infraorbital articulatedwith the sphenotic; premaxilla without teeth; dentary with a medial processfor insertion of the intermandibularis muscle; presence of a "branchiostegal"cartilage; lateral opening of the gas bladder partially closed by a hollowposterior expansion of the pterotic-supracleithum; posterior processesof the cleithrum and coracoid sutured lateroventrally behind the pectoral-fininsertion; basipterygium elevated medially; anterior external process ofthe basipterygium transformed into a lateral lamina; anterior inner processof basipterygium with a dorsal laminar expansion; ischiatic process ofthe basipterygium divided in a dorsal and a ventral portion; presence oftwo longitudinal rows of bony plates between head and tail. For a completelist of synapomorphies and a discussion of the evolution of the characterssee Reis (1993, 1996).
The Neotropical family Callichthyidae is found in most South Americanriver drainages (Paraná-Paraguay, São Francisco, AtlanticCoastal basins in Brazil, Amazonas, Orinoco, Maracaibo, Magdalena), aswell as in a few rivers in Panama, as shown in red in the figure below.They present highest diversity in the headwaters of the Amazonas drainageand those rivers draining the Guianan shield.
Evolution and Systematics
Discussion of Phylogenetic Relationships
The superfamily Loricarioidea is one of the best studied groups of the Siluroidei (Lundberg & Baskin, 1969; Howes, 1983; Schaefer & Lauder, 1986; Schaefer, 1988, 1990; Pinna, 1992). It is composed of six families and is currently diagnosed by the derived presence of a reduced swimbladder, encapsulated in expansions of the parapophysis of the first vertebrae, and of odontodes, small dermal denticles. The Loricariidae are more closely related to the Astroblepidae, which has been included as a subfamily of the Loricariidae in the past. Together, they represent the sister-group of the Scoloplacidae, a small family formed by four miniature species. This clade is the sister-group to the family Callichthyidae. The four families above form the "advanced Loricarioidea" and represent the sister-group of a clade formed by Nematogeneidae, with one single species in southern Chile, plus Trichomycteridae.
The monophyly of the family Callichthyidae is supported by several derived features, some of which are described above. The two subfamilies, Callichthyinae Hoedeman (1952) and Corydoradinae Hoedeman (1952), are each supported by several synapomorphies. The subfamily Corydoradinae presents Aspidoras as the sister group to a clade formed by Corydoras and Brochis. Both Aspidoras and Brochis are supported by a number of synapomorphies, but no one single derived feature was found to be shared by the species of Corydoras. The fact that no synapomorphies were found to diagnose Corydoras, as traditionally defined (Gosline, 1940), suggests that this genus is paraphyletic. The paraphyletic nature of Corydoras, however, is a consequence of recognizing Brochis as a separate genus, and additional phylogenetic work in this clade is necessary before a revision of Corydoras can be made. In the subfamily Callichthyinae some taxonomic and nomenclatural changes have already been made. It was found that Hoplosternum was also a paraphyletic assemblage. Two new genera were erected to keep each clade monophyletic. Hoplosternum in the "sensu stricto" is the sister group of Dianema. Two other species formerly assigned to Hoplosternum, the Hoplosternum thoracatum Group, represent the sister taxon to the above clade, and were transferred to the genus Megalechis. Four other species composing the Hoplosternum pectorale Group, are the sister taxon to the above clade, and were transferred to the genus, Lepthoplosternum. Callichthys, with only one currently recognized species, C. callichthys, is the most basal member of the callichthyines. The controversial genera Cascadura Ellis, 1913 and Cataphractops Fowler, 1915 were found to be synonyms of Hoplosternum.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimen Records: 1402
Specimens with Sequences: 944
Specimens with Barcodes: 933
Species With Barcodes: 109
Public Records: 85
Public Species: 15
Public BINs: 17
Callichthyidae is a family of catfishes (order Siluriformes), called armored catfishes due to the two rows of bony plates (or scutes) running down the length of their bodies. This family contains some of the most popular freshwater aquarium fish, such as the species of Corydoras.
The family derives its name from the Greek words kallis (beautiful) and ichthys (fish). Callichthyidae is one of six families in the superfamily Loricarioidea. It is sister to a clade formed by Scoloplacidae, Astroblepidae, and Loricariidae. Within the family Callichthyidae, the two subfamilies have eight genera and about 177 species. They account for about 7% of all catfish. Most of these species are in the genus Corydoras, the largest catfish genus.
The subfamily Corydoradinae includes about 90% of the species in the family Callichthyidae and is one of the most diverse siluriform assemblages in the Neotropics, with about 170 valid species. It includes two tribes, Aspidoradini and Corydoradini. Aspidoradini contains Aspidoras and Scleromystax, while Corydoradini contains Corydoras and Brochis. Some believe the genus Brochis should be synonymized with Corydoras.
The subfamily Callichthyinae contains Callichthys, Dianema, Hoplosternum, Lepthoplosternum, and Megalechis. According to a 1997 paper, Callichthys is the most basal member of the subfamily. In a 2004 study, different relationships among the callichthyines were found: Dianema and Hoplosternum form the most basal clade, and Callichthys is sister to Lepthoplosternum and Megalechis.
The first known fossil species of callichthyid is Corydoras revelatus from Salta, Argentina, of the late Paleocene. This species is tentatively placed in Corydoras, but is unambiguously a member of the subfamily Corydoradinae. It indicates that the lineages leading to the two callichthyid subfamilies occurred at least by the late Paleocene. It also suggests an earlier differentiation of loricarioids in comparison to other catfishes, or a lack of older fossils of other Neotropical groups.
The Neotropical family Callichthyidae is found in most South American river drainages (Paraná-Paraguay, São Francisco, Atlantic Coastal basins in Brazil, Amazon, Orinoco, Maracaibo, Magdalena). Hoplosternum punctatum is the only species in Central America, as it occurs in a few rivers in Panama. Callichthyidae present the highest species richness in the headwaters of the Amazonas drainage and those rivers draining the Guiana Shield.
The subfamily Corydoradinae is found east of the Andes and north of the Rio de La Plata system. Representatives of the Corydoradinae are found in several freshwater environments, ranging from fast-flowing piedmont streams with sandy or rocky bottoms to lowland pools with muddy bottoms.
Callichthyids are fairly small catfish, and range in size from some tiny Corydoras species that do not exceed 2 cm (0.79 in) to Hoplosternum littorale, which some sources list as growing to a length of up to 24 cm (9.4 in) TL. The mouth is small and ventral with one or two pairs of well-developed barbels. The dorsal and pectoral fins have strong spines, and a spine is found at the anterior border of the adipose fin.
The scutes that give these fish their name are one of the most obvious characteristics of these fish. The body has two rows of overlapping bony plates on each side. These plates are arranged so they overlap along the rows, as well as between the rows, giving full protection, but at the same time allowing some freedom of movement. These scutes connect with the solid bones of the head, and the head itself may be covered with bony plates. The upper row of lateral scutes may either meet on the back or a narrow bare area may be filled in with small oval or roundish bony platelets.
Species of the Corydoradinae are of small size (maximum about 9 cm (3.5 in) in standard length) and are easily distinguished from other callichthyids by their deep bodies and short maxillary barbels.
Living habits are varied; the family includes both bottom-foraging and midwater species. Callichthyids inhabit a wide range of habitats, from small, swift, oxygen-rich creeks to big rivers and flooded areas. Their habitats may even include swampy and muddy habitats where oxygen may be virtually absent. Callichthyids survive in these conditions by breathing air; air is collected at the water surface and swallowed. The intestines are used to absorb oxygen, and the air is expelled from the anus. The anterior digestive intestine packages digesta into a string of slightly compressed boluses, creating an air channel in the digestive intestine, thus allowing air to pass unimpeded. The posterior intestine is modified for respiration into a thin-walled and highly vascularized structure by reduction of the thickness of the epithelium, submucosa, and muscle layers; though highly modified to absorb air, it is inefficient for digestive purposes. Air moving through the digestive tract facilitates the movement of digesta to the rectum. Unlike other catfish such as loricariids or trichomycterids that may breathe air only under hypoxic conditions, callichthyids breathe air under all water conditions. Some callichthyids are able to absorb air through their hind guts to move short distances on land. Air stored in their digestive tracts also accounts for 75% of the necessary air for neutral buoyancy.
Breeding habits are also variable. Corydoradines breed over the substrate (such as rocks, logs, or leaves) as most catfish. However, the members of the subfamily Callichthyinae are known for building and guarding floating foam bubble nests; Hoplosternum littorale is reported to have the most complex nest structure. These floating nests are made of foam and plant debris. Spawning and caring for the eggs and larvae takes place in these nests. Parental care in callichthyines is by the male. In Corydoras and Hoplosternum, fertilization of eggs involves 'sperm drinking'; the female and male form the "T-position" with the female's mouth over the male's genital opening, and then the female drinks the sperm, releasing the sperm and eggs simultaneously.
Relationship to humans
Some species are quite common in South America and are fished commercially. They are usually cooked in their bony armor. Some callichthyids, especially species of Corydoras, are popular as ornamental fish in the fishkeeping hobby.
|Wikimedia Commons has media related to Callichthyidae.|
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