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. 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 in 1862.
In 2007, this genus was reviewed, validating five species. S. lima and S. trigonocephalus are redescribed in this paper. This genus is monophyletic.
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. 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. 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.