Teleocichla preta, a new species of cichlid from the Rio Xingu Basin in Brazil (Teleostei: Cichlidae).

Teleocichla preta nov. sp. inhabits the rapids along the Rio Xingu and lower portion of the Rio Iriri. It is the largest species in the genus, reaching 121·3 mm standard length (LS ) while others do not reach more than 87·8 mm LS . Teleocichla preta is distinguished from all other species of Teleocichla by the unique blackish (in live specimens) or dark brown (preserved specimens) overall colouration of the body, which masks the faint vertical bars or zig-zag pattern of blotches on the flanks. Teleocichla preta also has a deeper body and a deep laterally compressed caudal peduncle, unlike any other congener, as well as a stout lower pharyngeal tooth plate bearing molariform teeth on its median area.

Habitat structural complexity and morphological diversity of fish assemblages in a Neotropical floodplain river.

High species richness and evenness in structurally complex habitats has been hypothesized to be associated with niche partitioning. To test this idea, relationships between habitat structural complexity in river littoral-zone habitats and morphological diversity of tropical fishes were examined in the Cinaruco River, Venezuela. Six habitat attributes were quantified in 45 sites spanning a range of structural complexity. Fishes were collected during day and night to estimate species density and relative abundances at each site. Twenty-two morphological variables were measured for each species. Principal components analysis (PCA) of physical habitat data yielded two axes that modeled >80% of variation across sites. The first two axes from PCA of fish morphological variables modeled >70% of variation. Species density during both day and night was negatively associated with flow velocity and positively associated with habitat complexity. Similarity of day and night samples from the same site was significantly greater for sites with high habitat complexity and low flow. In general, mean local assemblage morphological PC scores were not significantly associated with habitat PC scores. Average, maximum, and standard deviation of morphological Euclidean distances of local assemblages revealed positive associations with structural complexity and negative associations with flow. These relationships held even when the positive relationship of species density was statistically removed from assemblage morphological patterns. Findings suggest that both species niche compression and assemblage niche space increase when habitat complexity is greater and flow velocity is lower in this tropical lowland river.