FISH SPECIES-DIVERSITY IN SAND BANK HABITATS OF A NEOTROPICAL RIVER

The fish fauna of the Cinaruco River, an intermediate sized floodplain river that forms the southern boundary of the newly established Santo s Luzardo National Park in the llanos of Venezuela, was sampled in 199 3-1994. Due to highly reasonal rainfall, the nutrient-poor Cinaruco un dergoes dramatic changes in water level, creating a variety of seasona lly available habitats for fishes. Sand bank habitats are conspicuous features in both main-channel and lentic backwater areas, and support fish assemblages that are different from adjacent rocky shore and shru bby shore habitats. Seine samples from sand bank habitats revealed hig h alpha diversity, dom inated numerically by a few species of small Ch araciformes. Comparisons among and between lagoon, side channel. and m ain-channel sand bank habitats showed little assemblage similarity. Ov erall, sand bank habitats were used by 8 orders, 21 families, and 105 species of fish, mostly of size classes less than 100 mm. Several spec ies are currently undescribed. Elements which may contribute to high f ish diversity include proximity to a diverse Amazonian fauna, seasonal ly dynamic habitat availability, the influence of keystone predators, and episodes of intermediate disturbance, such as seasonal release fro m intense biotic interactions.