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Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25°C) covering the normal seasonal range in the lower Parana´river and Rı´o de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight À1 h À1 at 15, 20 and 25°C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg À1 h À1 . Differences between sizes and between temperatures (except 15 vs. 20°C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125-350 ml individual À1 h À1 ) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Parana´watershed (up to over 200,000 ind m À2 ) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.

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