RESUMEN

About 1000 freshwater fishes have been found so far in the Orinoco River Basin of Venezuela and Colombia. This high ichthyological diversity reflects the wide range of landscapes and aquatic ecosystems included in the basin. Mountain streams descend from the high Andes to become rapid-flowing foothill rivers that burst out upon vast savannah flatlands where they slowly make their way to the sea. These white-water rivers are heavily laden with sediments from the geologically young Andes. Because their sediment deposits have formed the richest soils of the basin, they have attracted the highest density of human populations, along with the greatest levels of deforestation, wildfires, agricultural biocides and fertilizers, sewage and all the other impacts associated with urban centres, agriculture and cattle ranching. In the southern portion of the basin, human populations are much smaller, where often the only inhabitants are indigenous peoples. The ancient rocks and sands of the Guiana Shield yield clear and black water streams of very different quality. Here, sediment loads are miniscule, pH is very acid and fish biomass is only a fraction of that observed in the rich Andean tributaries to the north. For each region of the basin, the current state of knowledge about fish diversity is assessed, fish sampling density evaluated, the presence of endemic species and economically important species (for human consumption or ornamental purposes) described and gaps in knowledge are pointed out. Current trends in the fishery for human consumption are analysed, noting that stocks of many species are in steep decline, and that current fishing practices are not sustainable. Finally, the major impacts and threats faced by the fishes and aquatic ecosystems of the Orinoco River Basin are summarized, and the creation of bi-national commissions to promote standardized fishing laws in both countries is recommended.

Asunto(s)

Conservación de los Recursos Naturales , Ecosistema , Peces , Ríos , Agricultura , Animales , Bovinos , Explotaciones Pesqueras , Agua Dulce , Humanos , Venezuela

RESUMEN

Este trabajo presenta la descripción de una nueva especie del género Bryconops Kner(1858) para la cuenca del Río Negro en Brasil y Venezuela. Bryconops disruptus posee los caracteres que la asocian a las especies del grupo Bryconops (sensu stricto), con el maxilar edéntulo y corto. Sin embargo, se diferencia de B. alburnoides, B. caudomaculatus y Brycochandus durbini, en poseer la línea lateral incompleta con menos de 25 escamas con poro, mientras que las otras especies tienen la línea lateral extendida hasta al menos el origen del pedúnculo caudal

Asunto(s)

Animales , Fauna Acuática , Peces/clasificación , Brasil , Venezuela

RESUMEN

Fossil fishes from the Miocene La Venta fauna of the Magdalena River Valley, Colombia, are identified as Colossoma macropomum (Characidae), a living species from the Orinoco and Amazon basins. The fossils document a long and conservative history for a species that is highly specialized for feeding on streamside plants. The phylogenetically advanced position of Colossoma in the subfamily Serrasalminae implies that six related genera and other higher characid taxa originated well before 15 million years ago. This discovery also corroborates neontological evidence for a vicariance event that contributed species from Miocene Orinoco-Amazon faunas to the original Magdalena region fauna. The fossils suggest a formerly diverse Magdalena fauna that has suffered local extinction, perhaps associated with late Cenozoic tectonism. This new evidence may help explain the depauperate nature of the modern Magdalena River.