Abstract

FERNANDEZ, LUIS  and  BECHARA, JOSÉ A.. AN ASSESSMENT OF FISH COMMUNITIES ALONGA PIEDMONT RIVER RECEIVING ORGANIC POLLUTION(ACONQUIJA MOUNTAINS, ARGENTINA). Acta biol.Colomb. [online]. 2010, vol.15, n.2, pp.79-100. ISSN 0120-548X.

The relationships between fish assemblage structure and environmental variables along a pollution gradient in the Medina River were analyzed over a year in four sampling sites (S1-S4). The river flows in a mountain-plain transition and is affected by several small town wastewater and sugar cane industries effluents. Environmental variables were divided in two sets, hereafter named -pollution- and -natural-. The first set included water quality variables modified by anthropogenic activities such as D.O. (Dissolved Oxygen), C.O.D. (Chemical Demand Oxygen), and dissolved ion concentrations. Natural variables included altitude, position, and time of the year. The upstream site (S1) had the lowest species richness and C.P.U.E. (catchperunitofeffort). The number of species and density increased downriver(S2-S3). S1 was inhabited by an invertivor especies (Trichomycteruscorduvensis) that has low tolerance to adverse environmental conditions, and has high D.O. requirements. S4 sustained the most tolerant and abundant species (Otocinclus vittatus, Corydoras paleatus), which endure the lowest D.O. and the highest C.O.D. A Canonical Correspondence Analysis for natural variables showed a significant gradient of species composition related to altitude and discharge. Water quality degradation by sugar cane factories and urban development, coupled with natural climatic, topographic and hydrological factors explained a significant amount of spatial and temporal variation in fish community structure (48%). Natural and pollution variables shared about 15% of total variance. However, pollution variables were not significant after partitioning out the effects of natural variables. Natural variability remained significant after removal of pollution effects.

Keywords : organic pollution; river gradients; Neotropical fish; canonical analyses; environmental factors.

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