Longitudinal structure, density and production rates of a neotropical stream fish assemblage: the river Ubatiba in the Serra do Mar, southeast Brazil

Spatio-temporal variations in the structure, density, biomass and productio n rates of fish were assessed in the neotropical River Ubatiba (Serra do Ma r, southeast Brazil). Electrofishing techniques and the length-frequency me thod were shown to be reliable for the assessment of fish numbers and produ ction rates in these running waters of medium conductivity. Eighteen fish s pecies of small size and prolonged spawning period were broadly distributed throughout the river catchment. Over the year, the assemblage structure wa s persistent along the river. Water column omnivore and algae/detritivore s pecies dominated in density (15086-70330 ind. ha(-1)), whereas three omnivo res and a piscivorous species accounted for 70% of the production (51.5-250 .4 kg ha(-1) yr(-1)). Comparison of production rates among, tropical, tempe rate and Mediterranean stream fish assemblages indicate lower rates in trop ical streams and an inverse relationship between production and species div ersity, lower production rates in high-diversity tropical streams vs higher rates in low-diversity Mediterranean streams, with intermediate rates in t emperate streams of intermediate diversity.