Scientists have found three new species of electric knifefishes living in the Amazon in Brazil.
The new species are all members of the gymnotiform sternopygid genus Rhabdolichops and were caught in the lowland central Amazon region. The group are commonly referred to as glass knifefishes.
Sandra Correa, William Crampton and James Albert described the new species in Copeia, the journal of the American Society of Ichthyologists and Herpetologists, and have named them Rhabdolichops nigrimans, R. navalha and R. lundbergi.
Rhabdolichops nigrimans and R. navalha are currently known only from the very soft and acidic blackwater river systems, while lundbergi lives in the slightly less hostile whitewaters of the main river channels and floodplain channels.
According to the paper, R. nigrimans and R. lundbergi are closely related sister species that sit within a clade that is separate from other Rhabdolichops species. Their grouping is believed to be between Eigenmannia and Rhabdolichops.
Like many members of the Gymnotiformes, some striking sexual dimorphism is seen in some members, with males of R. nigrimans bearing significantly longer caudal fins than females.
The other blackwater species, R. navalha, is believed to be a sister species to R. stewarti. This knifefish also has a unique type of electric organ among the Gymnotiformes:
"Rhabdolichops navalha exhibits a unique morphology of the electric organ where the posterior margin ends abruptly and is replaced posteriorly by rigid and transparent non-electrogenic tissue."
The members of the Rhabdolichops genus typically reach a size of around 30cm/12" and predominantly live in the deep water channels of rivers in the Amazon and Orinoco basin, where they feed upon aquatic invertebrates, such as copepods.
The deeper waters of the river channels are poorly studied, compared to the shallow waters, and contain many species of endemic fishes. It is widely believed that many new species of deepwater fishes remain undescribed in this unusual habitat.
The Rhabdolichops genus currently contains another eight species including: R. caviceps, R. eastwardi, R. electrogrammus, R. jegui, R. troscheli, R. zareti and R. longicaudatus.
For more information see the paper: Correa SB, Crampton WGR and JS Albert (2006) - Three New Species of the Neotropical Electric Fish Rhabdolichops (Gymnotiformes: Sternopygidae) from the Central Amazon, with a New Diagnosis of the Genus. Copeia: Vol. 2006, No. 1, pp. 27-42.