A New Species of Cascudinho of the Genus Hisonotus (Siluriformes: Loricariidae: Hypoptopomatinae) from the Upper Rio Tapajos Basin, Brazil

Hisonotus bockmanni, new species, is described based on specimens collected in a sandbank in the Rio Cururu, a tributary to the Rio Teles Pires, one of the rivers forming the Rio Tapajos in the Amazon Basin. The new taxon is distinguished from its congeners by a unique color pattern, whose most striking features are: two elliptical white spots, anterior to nostrils; predorsal region darkly pigmented with five unpigmented spots arranged as anteriorly pointed chevron; and a rostrocaudally elongate cross along most of the caudal peduncle. The placement of the new species in Hisonotus as well as its possible affinities within that genus are discussed in light of the current knowledge of the phylogenetic relationships among the Hypoptopomatinae.

Self-potential signals from an analog biogeobattery mode

A tank experiment was conducted to check if self-potential (SP) signals can be generated when buried organic matter is wire-connected to a near-surface, oxygen-rich, sediment layer. This experiment demonstrated that once wired, there was a flux of electrons (hence an electric current) between the lower and upper layers of the sandbox with the system responding as a large-scale microbial fuel cell (a type of bioelectrochemical system). An electric current was generated by this process in the wire and the SP method was used to monitor the associated electric potential distribution at the top of the tank.. The electric field was controlled by the flux of electrons through the wire, the oxidation of the organic matter, the reduction of oxygen used as a terminal electron acceptor, and the distribution of the DC resistivity in the tank. The current density through the wire was limited by the availability of oxygen and not by the oxidation of the organic matter. This laboratory experiment incorporated key elements of the biogeobattery observed in some organic-rich contaminant plumes. This analogy includes the generation of SP signals associated with a flux of electrons, the capacity of buried organic matter in sustaining anodic reactions, network resistance connecting terminal redox reactions spatially separated in space, and the existence of anodic secondary coupled reactions. A resistivity tomogram of the tank, after almost a year in operation, suggests that oxidative processes triggered by this geobattery can be imaged with this method to determine the radius of influence of the bioelectrochemical system.