A review of the South American shovelnose catfish Sorubim has recognised five species as valid.
Michael Littmann of the Field Museum of Natural History in Chicago, says that Sorubim lima, S. maniradii, S. trigonocephalus, S. elongatus and S. cuspicadus are all valid species.
Littman, who published his findings in the latest issue of Zootaxa, examined hundreds of non-type specimens of the genus and redescribed Sorubim lima and the rare S. trigonocephalus on the basis of the new material he studied.
Sorubim lima and S. trigonocephalus were described in 1820 and 1920 respectively, but the other three species have all been described between 2000 and 2001.
At least two of the catfishes - Sorubim lima and S. elongatus - commonly appear in the aquarium trade, where they are sold as Sorubim lima. All are relatively similar in colour pattern.
Sorubim maniradiiSorubim maniradii was described by Littmann, Burr and Buitrago Suarez in 2001, and was discovered in the Rio Napo and Rio Yasumi drainages of Napo State in Ecuador.
It is superficially similar in overall appearance to S. lima. The name maniradii comes from the Latin for many radii and refers to the high number of gill rakers seen in the species compared to other members of the genus. S. maniradii typically has 31-37 rakers, compared to just 13-23 seen in other Sorubim species.
Sorubim elongatusSorubim elongatus, the Slender shovelnose catfish, was described by Littman, Burr and Isern in 2001 and sometimes appears for sale in the aquarium trade, where it is sold as Sorubim lima.
As the name suggests, it is much more elongate than other members of the Sorubim genus - both in the head and the body, giving it a very slender appearance.
It has eight branched pectoral fin rays, 22 anal-fin rays, small unjoined patches of vomerine teeth and a body and head which appears cylindrical in cross section.
Littmann says that most specimens of S. elongatus have been caught in the main channels and lower reaches of the Amazon, Essequibo and Rio Orinoco basins, but specimens have also been caught in the Rio Mamore.
Sorubim limaLike other Sorubim species, S. lima is quite widely distributed. Littmann says that the species is the most widely distributed in the genus, being found east of the Andes from the Amazon, Orinoco, Parana and Parnaiba basins.
It is syntopic with S. elongatus and S. maniradii in the upper Amazon in Brazil, Peru, Bolivia and Ecuador.
Littmann says that, apart from the tail, the species is most similar in morphology to cuspicaudus: "It differs from S. cuspicaudus in the following ways (S. cuspicaudus in parentheses): lower lobe of caudal fin rounded (pointed and straight); body short and stout (elongated); no posterior fontanelle groove on the supraoccipital bone (groove present).
"In live specimens, lighter areas may appear golden or slate grey, often appearing iridescent. Some invdividuals may also display dark blotches or spots on the dorsal part of the body. Ventral part of body white or cream coloured.
"Juveniles more heavily pigmented than adults. Posterior-most rays on dorsal, anal, and pelvic fins heavily speckled with chromatophores, speckling reduced in adults."
Sorubim trigonocephalusSorubim trigonocephalus was described by Miranda-Ribeiro in 1920 and goes under the common name of Arrowhead shovelnose.
It is reportedly extremely rare in natural history collections and only three specimens have ever been collected; the fish came from the Rio Madeira and Rio Tapajos, which are tributaries of the Amazon.
It has a similar body shape to S. lima, and also has a similarly deep caudal peduncle and nin branched pectoral fin rays. Sorubim trigonocephalus can be told apart from other Sorubim by its very elongated snout, triangular head and an exposed patch of premaxillary teeth which is as wide as it is long.
The species gets its name trigonocephalus from the Latin "trigono" and "cephalus", which refers to the triangular shape of the head in dorsal or ventral view.
It reaches a maximum length of 50cm.
Sorubim cuspicaudusThe easiest of the five species to identify is Sorubim cuspicaudus, which has a caudal fin that is markedly different to those of other members of the genus.
While other Sorubim have a very round lower lobe and a curved upper lobe, Sorubim cuspicaudus has an almost straight, elongate and deeply forked tail. The species name cuspicaudus means "pointed tail" in Latin.
The species was described in 2000 by Littmann, Burr and Nass and is found in the northern Colombia in the far north west of South America, where it occurs in Lake Maracaibo and the Rio Sinu and Rio Magdalena basins.
HabitatsAlthough Sorubim are widely regarded as white water fish, Littmann says that members of the genus are also found in lakes and streams alongside main river channels.
The species are typically found over substrates of mud, sand and clay and are often associated with vegetation, particularly roots, grasses and reeds.
Little is known about their biology, so most natural history observations have been made upon captive specimens. Says Littmann: "Near Iquitos, Peru, I observed juvenile Sorubim among branches, sticks, root masses and reed-like grasses in small canos, tributary streams and backwaters of large river channels.
"The darker fin pigmentation and longer fin-ray filaments of juveniles may provide camouflage while hiding in grasses and leaf detritus. Larger adults living in more open-water habitats lose these cryptic features.
"I have collected Sorubim mainly in turbid small streams and large rivers with aquatic vegetation and little or no flow, but only occasionally in clearer black water or over a strictly sand or mud-bottomed substrate."
For more information see the paper: Littmann MW (2007) - Systematic review of the neotropical shovelnose catfish genus Sorubim Cuvier (Siluriformes: Pimelodidae). Zootaxa, 1422: 1-29.