Sorubim

''Sorubim'' is a small genus of long-whiskered catfish native to tropical South America. A number of characteristics allows the differentiation of each species in the genus. ''Sorubim'' species are important food fish in South America and are highly significant to fisheries of some areas; however, harvests of these fish are not identified as much as other, more popular food fishes such as ''Colossoma'', '' Arapaima'', and ''Brachyplatystoma''. Some species of this family are popular aquarium fish.

Taxonomy

The genus name is derived from a Brazilian local name, ''sorubí''.Littman, M.W. (2007): page 4 The description of ''Sorubim'' has been attributed to both Cuvier and Agassiz in 1829, but because Cuvier's description predates that of Agassiz by two months, Cuvier's is valid. Later, ''Sorubim lima'', originally described as ''Siluris lima'' in 1801, was designated as the type species by Bleeker.

Species

The currently recognized species in this genus are:
* ''Sorubim cuspicaudus'' Littmann, Burr & Nass, 2000 (trans-Andean shovelnose catfish)
* '' Sorubim elongatus'' Littmann, Burr, Schmidt & Isern, 2001 (slender shovelnose catfish)
* ''Sorubim lima'' (Bloch & Schneider, 1801) (duckbill catfish)
* ''Sorubim maniradii'' Littmann, Burr & Buitrago-Suárez, 2001
* ''Sorubim trigonocephalus'' Miranda-Ribeiro, 1920 (arrowhead shovelnose catfish)

Distribution and habitat

''Sorubim'' is a widely distributed genus, collected from many major river basins in 10 countries.Littman, M.W. (2007): page 1 ''S. lima'' is the most widely distributed species of the genus, found east of the Andes in the Amazon, Orinoco, Paraná, and Parnaíba basins. Initially it did not occur in the upper Paraná basin above the Guaíra Falls, but these disappeared after the construction of the Itaipu Dam, allowing this species (and several others) to spread. It is syntopic with ''S. elongatus'' in the Orinoco basin and with ''S. elongatus'' and S. ''maniradii'' in the upper Amazon drainage of Brazil, Ecuador, Peru, and Bolivia. ''S. maniradii'' was discovered in the Napo and Yasuni River drainages of Ecuador, but also occurs in other tributaries of the Amazon. ''S. elongatus'' is found in the Amazon, Orinoco, and Essequibo River basins. ''S. cuspicaudus'' is found in northern Colombia and inhabits Lake Maracaibo, Sinu River, Cauca River, and Magdalena River basins. ''S. trigonocephalus'' was initially considered very rare as only three specimens were known by 2007. Later many more specimens have been collected and the species is relatively common. It is found only in the Tapajós and Xingu basins in Brazil. The type locality of ''S. trigonocephalus'' has been reported as the Madeira River, but the species does not occur there and the correct locality is now recognized to be the Arinos River, a part of the Tapajós basin.

''Sorubim'' species are found in fast-moving and slow-moving waters, including lakes, rivers, and bays. Typically, the substrate is either sand, clay, or mud, associated with reeds, grasses, and roots. They are not found as often over substrates of strictly sand or mud. They are also not found as commonly in clearer blackwater habitats. ''S. elongatus'' occurs in both whitewater and blackwater, found in floodplain lakes and small creeks to large rivers. ''S. lima'' is commonly found in schools.

Anatomy and appearance

''Sorubim'' species, like other catfish, possess dorsal and pectoral fin spines. They have a triangular adipose fin. As Pimelodidae, these fish have very long barbels, especially maxillary barbels, which range in length from reaching the pectoral fin to extending past the pelvic fins.Littman, M.W. (2007): page 3 Like some other pimelodid genera, these fish may have long filaments on their dorsal, pectoral, and caudal fins; in juveniles, these filaments may be even longer than the body. ''Sorubim'' is characterized by a shovel-like, projecting upper jaw with an exposed, villiform (brush-like) premaxillary tooth patch. The head is depressed and usually three times longer than it is wide. The eyes are set laterally and usually visible from below. They have a characteristic black, lateral stripe, variable in width, that extends from the snout to the end of the caudal fin; though this may seem minor, no other pimelodid has a lateral stripe that reaches down the entire length of the head and body.

Along with the lateral stripe, ''Sorubim'' species have a darkened dorsal surface, which is sometimes separated by a thinner, lighter-colored band. The dorsal surface may change its shade quickly with its surroundings. ''S. lima'' may also display dark blotches or spots on its dorsal surface. The ventral part of the body is white or cream-colored. Light areas may appear golden or slate gray, often appearing iridescent. Young fish are more heavily pigmented than adults. Posterior-most rays on dorsal, anal, and pelvic fins are elongated, darker, and heavily speckled with chromatophores; however, this speckling is reduced in the adults. This could provide camouflage when the fish are young and hiding among plant materials, and is lost when the adults live in more open water habitats.

''S. lima'' appears similar to ''S. trigonocephalus''; however, the latter has a long snout, pointed (triangular) head, and an exposed patch of premaxillary teeth that is as wide as it is long. ''S. cuspicaudus'' has a markedly different tail (straight, pointed, and long) in contrast to the other ''Sorubim'' with more rounded caudal fin lobes. ''S. maniradii'' is differentiated from the other species by a high number of gill rakers, ranging from 31–37, compared to the 13–23 of the other ''Sorubim'' species, as well as a more diffused lateral stripe. ''S. elongatus'' has an elongated head and body, and appears rather slender in comparison to the other members of this genus.

''S. cuspicaudus'' is the largest species in the genus, reaching up to in standard length. ''S. trigonocephalus'' and ''S. lima'' reach a length of almost . By contrast, ''S. elongatus'' and ''S. maniradii'' only reach about half that length, about in the former and in the latter.

Ecology

Because of the natural whitewater habitats of these fish, which makes natural observation difficult, most observations of the behavior of this fish is largely known from study of fish in aquaria. Natural history and reproduction of this fish are not well known. When inactive, these fish often swim in a vertical posture, probably to help blend into stems of reeds and other aquatic plants; when active, they swim in a normal, horizontal manner. They may use this camouflage either to hide from predators or as part of ambush predation. These fish feed on fish and crustaceans, and as adults are largely piscivorous. ''Sorubim'' species have been observed in captivity to excavate a small pit as a nest and even to guard freshly hatched young (unfortunately, none of these young survived).

These fish are nocturnal and occur in groups or schools.

In the aquarium

''S. lima'' has been in the aquarium trade for many years, and is the most common species found in the aquarium trade. ''S. elongatus'' also appears rather often, and is sold as ''S. lima''.

This fish is lazy and slow-moving; being nocturnal, it will usually hide during the day. It will accept most food, but also can consume smaller fish. It is hardy, and the pH is not of great importance, but slightly acidic is best. This fish requires a large aquarium. This fish prefers a current as well as clean water. It has not yet been bred in captivity.

References

{{Taxonbar, from=Q3491316

Pimelodidae
Fish of the Amazon basin
Fish of South America
Catfish genera
Taxa named by Georges Cuvier
Freshwater fish genera