We evaluated the water characteristics and particle sedimentation in Macrobrachium amazonicum (Heller 1862) grow-out ponds supplied with a high in£ow of nutrient-rich water. Prawns were subject to di¡erent stocking and harvesting strategies: upper-graded juveniles, lower-graded juveniles, non-graded juveni-les1selective harvesting and traditional farming (non-grading juveniles and total harvest only). Dissolved oxygen, afternoon N-ammonia and N-nitrate and soluble orthophosphate were lower in the ponds in comparison with in£ow water through the rearing cycle. Ponds stocked with the upper population fraction of graded prawns showed higher turbidity, total suspended solids and total Kjeldahl nitrogen than the remaining treatments. An increase in the chemical oxygen demand:biochemical oxygen demand ratio from inlet (4.9) to pond (7.1^8.0) waters indicated a non-readily biodegradable fraction enhancement in ponds. The sedimentation mean rate ranged from 0.08 to 0.16 mm day À 1 and sediment contained 480% of organic matter. The major factors a¡ecting pond ecosystem dynamic were the organic load (due to primary production and feed addition) and bioturbation caused by stocking larger animals. Data suggest that M. amazonicum grow-out in ponds subjected to a high in£ow of nutrient-rich water produce changes in the water properties, huge accumulation of organic sediment at the pond bottom and non-readily biodegradable material in the water column. However, the water quality remains suitable for aquaculture purposes. Therefore, nutrient-rich waters, when available, may represent a source of unpaid nutrients, which may be incorporated into economically valued biomass if managed properly.

The upper Paraná River basin drains areas of intensive industry and agriculture, suffering negative impacts. The Córrego Rico flows through sugar cane fields and receives urban wastewater. The aim of this work is to describe and to compare the fish assemblage structure in Córrego Rico. Six standardized bimonthly samples were collected between August 2008 and June 2009 in seven different stretches of Córrego Rico. Fishes were collected with an experimental seine and sieves, euthanized, fixed in formalin and preserved in ethanol for counting and identification. Data were recorded for water parameters, instream habitat and riparian features within each stretch. Non-metric multidimensional scaling, species richness and diversity analysis were performed to examine spatial and seasonal variation in assemblage structure. Fish assemblage structure was correlated with instream habitat and water parameters. The fish assemblage was divided in three groups: upper, middle and lower reaches. High values of richness and diversity were observed in the upper and lower stretches due to connectivity with a small lake and Mogi Guaçu River, respectively. Middle stretches showed low values of richness and diversity suggesting that a small dam in the middle stretch negatively impacts the fish assemblage. Seasonal differences in fish assemblage structure were observed only in the lower stretches.

The effects of artificial substrate and night-time aeration on the culture of Macrobrachium amazonicum were evaluated in 12 ponds stocked with 45 prawns m À2 . A completely randomized design in 2 9 2 factorial scheme with three replicates was used. The combination of factors resulted in four treatments: with substrate and aeration (SA), with substrate and without aeration (SWA), without substrate and with aeration (WSA) and without substrate and aeration (WSWA). The presence of substrate in SA and SWA treatments reduced suspended particles (seston) by~17.3% and P-orthophosphate by~50%. The use of aerator (WSA and SA treatments) significantly (P < 0.05) increased the concentration of dissolved oxygen, suspended particles and nutrients in the pond water. These results indicate that the effect of substrate on turbidity and total suspended solids (TSS) values is opposite to the effect of the aerator. The aerators in semiintensive grow-out M. amazonicum farming lower water quality because they increased the amount of detritus and nutrients in the pond water. On the other hand, the use of artificial substrate reduces turbidity values, chlorophyll a, TSS and P-orthophosphate concentrations. Therefore, the combination of substrate addition and night-time aeration is not interesting because they have opposite effects.

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