New Entomocorus named in review

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Scientists have reviewed the South American catfish genus Entomocorus and have named a new species.

Roberto Reis and Thiago Borges reviewed the auchenipterid genus Entomocorus in the latest issue of the ichthyological journal Copeia and recognised four species, including one which is new to science.

According to the study, Entomocorus benjamini is found in the Rio Madeira, Entomocorus gameroi is found in the Rio Orinoco, Entomocorus melaphareus is found in the lower Rio Amazonas, while the fourth species, which has been named Entomocorus radiosus, occurs in the upper Rio Paraguay.

Entomocorus radiosusThe new species is believed to be endemic to the Mato Grosso Pantanal area of the upper Rio Paraguay and reaches a size of around 4-5cm, according to the type series.

Reis and Borges said that the new species can be differentiated from other Entomocorus by the following combination of characters: "Entomocorus radiosus is diagnosed by the unique combination of a long anal-fin base, 18-22 branched anal-fin rays, unpigmented pectoral and pelvic fins, and caudal fin hyaline, with distal half of dorsal and ventral lobes pigmented with black."

The species is believed to feed primarily on microcrustaceans, such as cladocerans, copepods and ostracods, but stomach content analyses have also revealed insects, fish eggs and detritus.

EntomocorusThe four Entomocorus can be differentiated by the melanin patterns seen on their tail fins.

Entomocorus benjamini has a black edge to the posterior margin, which is thickest at the top; Entomocorus radiosus has a thicker black edge to the posterior margin of the caudal fin; Entomocorus gameroi has a black diagonal line running through the caudal extending from the top of the caudal peduncle to the just above the middle of the tail, while E. melaphareus has a small black spot of black on the upper lobe.

The genus is known for its striking sexual dimorphism, which is very prominent in E. radiosus, E. melaphareus and E. gameroi: "Transformed males have stiff, ossified maxillary barbels, an elongated dorsal-fin spine, ventrally-directed pectoral-fin spine hooks, very elongated pelvic-fin unbranched rays, and a rotated anal-fin base.

No transformed males of E. benjamini have been examined so far, and it is uncertain whether males of this species ever transform in a manner similar to that in the other three species.

For more information see the paper: Reis RE and TAK Borges (2006) - The South American Catfish Genus Entomocorus (Ostariophysi: Siluriformes: Auchenipteridae), with the Description of a New Species from the Paraguay River Basin. Copeia, 2006(3), pp. 412-422