Fishes from the Las Piedras River, Madre de Dios basin, Peruvian Amazon

: We report results of an ichthyological survey on the Las Piedras basin, a tributary of the Madre de Dios River located in the southwestern portion of the Amazon Basin in southeastern Peru. Collections were made at low water (June, 2011) from 180 - 270 m elevation, within the Fitzcarrald Arch. This is the last of four expeditions to the region with the goal of comparing the ichthyofaunas across the headwaters of the largest tributary basins in the western Amazon: Juruá, Ucayali, Purús and Madre de Dios rivers. Twenty-one sites along the Las Piedras River and its tributaries were sampled and a total of 144 species belonging to 32 families and seven orders were captured and identified. The most diverse families were Characidae (34 spp.), Loricariidae (23 spp.),


Introduction
The Las Piedras River, also known as Tacuatimanu, is a white water river that rises in the inner portions of Fitzcarrald Arch and runs about 600 km until its mouth at the Madre de Dios River, upstream the town of Puerto Maldonado in Peru. The Fitzcarrald Arch is an area uplifted during the Pliocene (c. 4 Ma) in association with the subduction of the Nazca ridge (Espurt et al. 2007;2010). Hydrologically, the Las Piedras is classified as a mid-to lowland elevation river with no direct Andean influence (Thieme et al. 2007).
Biogeographically, the region is included within the Mamore-Madre de Dios Piedmont Freshwater Ecoregion of the World (FEOW-318;Abell et al. 2008). Some work has been done on the fish fauna of the Madre de Dios basin and its tributaries in Peru and Bolivia. At least 325 fish species are known from the Madre de Dios River (Barthem et al. 2003). Perhaps the most comprehensive study on the ichthyofauna of the Madre de Dios basin is the one of Barthem et al. (2003), which identified 287 species from the region near the mouth of the Los Amigos River in Peru and illustrated 158 species and their habitat characteristics. Several local studies describe the faunal particularities within Madre de Dios River drainage and their tributaries. Those present a fish diversity of 210 species for Manu River (Ortega, 1996); 232 species for Tambopata River (Chang 1998); 95 species to Pampas del Heath (Ortega, 1994); and 52 species for the Inambari River (Palacios and Ortega 2009). However, hitherto no studies have been published for the Las Piedras River.
Here we report the results of an expedition to the Las Piedras River as part of a four-year biodiversity survey project funded by NSF called "Proyecto Alto Purus". The aim of this project is to compare the ichthyofaunas of headwaters across four major basins of the Fitzcarrald Abstract: We report results of an ichthyological survey on the Las Piedras basin, a tributary of the Madre de Dios River located in the southwestern portion of the Amazon Basin in southeastern Peru. Collections were made at low water (June, 2011) from 180 -270 m elevation, within the Fitzcarrald Arch. This is the last of four expeditions to the region with the goal of comparing the ichthyofaunas across the headwaters of the largest tributary basins in the western Amazon: Juruá, Ucayali, Purús and Madre de Dios rivers. Twenty-one sites along the Las Piedras River and its tributaries were sampled and a total of 144 species belonging to 32 families and seven orders were captured and identified. The most diverse families were Characidae (34 spp.), Loricariidae (23 spp.), and Pimelodidae (19 spp.).  seine nets (5 and 10 m, 5 mm between knots), gill nets, dip nets, cast nets, hook and line, and trawl nets (3 m, 5 mm between knots) for sampling in deep portions of the Las Piedras River main channel. Electric fishes in streams and oxbow lakes were located with the aid of a portable amplifier (Crampton et al. 2007). A reference collection was accumulated with one or more representatives of all morphospecies encountered. Tissue samples were excised using a sterilized scalpel and preserved in 95% ethanol in 1.8 ml vials, and then stored in a cool location at the base camp before transport to the laboratory. All specimens were fixed in 10% formalin for at least 48 hours in a closed Nalgene container or covered flat plastic tray (for larger specimens), and later transferred to 70° GL ethanol.
Fish specimens were photographed alive or after storage in alcohol. Photo-tank pictures were taken following techniques explained by Sabaj-Pérez (2009) with a Panasonic Lumix DMC-FZ50 (10 Mega Pixels). Fishes were identified to the lowest taxonomic level possible, using available literature and help of specialists by photo identifications. The classification presented here is based on Reis et al. (2003) with some additional changes proposed by Sullivan et al. (2006)
A The Las Piedras River presents several species in common with the Paraná-Paraguay system, a pattern well known for the fish fauna from the upper Madeira tributaries (Kullander 1986 Lima and Ribeiro 2011). A large portion of the fish fauna from the Las Piedras River and Madre de Dios region is formed by species restricted to the foreland basin; e.g., Hypostomus unicolor, Steindachnerina guentheri, and Lamontichthys filamentosus (Vari 1991;Armbruster 2008;Paixão and Toledo-Piza, 2011). We tentatively identified 31 species (21% of the total) from the Las Piedras River restricted to the Amazon-Orinoco foreland, suggesting the importance of this area and its history in forming the regional species pool (Albert and Crampton 2010;Albert and Carvalho 2011;Lima and Ribeiro 2011).
We collected a large number of gymnotiform species (14 spp.) compared to previous inventories in the Amazon basin, probably due to use of trawl nets and portable amplifiers. In addition some species are for the first time referred for the Madre de Dios basin such as Acestrocephalus pallidus, Galeocharax goeldi, Roeboides descalvadensis, Xyliphius lepturus and Rhinodoras boehlkei, the last two captured only with trawl nets.
The sampled habitat with highest diversity was the "river", followed by the "stream" and the "oxbow lakes". Probably the use of trawl nets added an additional riverine assemblage of fish species, those inhabiting the bottom of the river channel. In the study by Barthem et al. (2003) 131 species were collected in oxbow lakes, contrasting with the 35 species registered herein in this kind of habitat. The fact that fewer species were caught in the oxbow lakes probably refers to the scarcity of this kind of habitat in the Las Piedras River basin, mainly in the upper portions of the river. Although a low number of species were collected in the "oxbow lakes" these species were highly restricted to this kind of habitat. Almost no species were shared by oxbow lakes and streams, except those generally regarded as widespread, e.g. Hoplias malabaricus and Astyanax spp.   Kullander, 1986 X Cichlasoma boliviense Kullander, 1983 X Crenicichla semicincta Steindachner, 1892 X X