The temporal variation of stoichiometry between consumed oxygen and oxidized carbon was investigated for the aerobic mineralization of leachates from aquatic macrophytes. Seven species of aquatic plants, viz. Cabomba piauhyensis, Cyperus giganteus, Egeria najas, Eichhornia azurea, Salvinia auriculata; Scirpus cubensis and Utricularia breviscapa, were collected from Ó leo lagoon located in the floodplain of MogiGuac¸u river (Sa˜o Paulo State, Brazil). After being collected, the plants were washed, oven-dried and triturated. In order to obtain the leachate, the fragments were submitted to an aqueous extraction (cold). Mineralization chambers were incubated at 20°C containing leachates dissolved in water samples from Ó leo lagoon to a final concentration of ca. 200 mg l )1 on carbon basis. The chambers were maintained under aerobic conditions; the concentrations of the organic carbon (particulate and dissolved) and the dissolved oxygen were measured during approximately 80 days. Elemental analysis of the detritus and the concentrations of the remaining material (DOC and POC) were used to determine the amounts of mineralized organic carbon. The data were analyzed with first-order kinetics models, from which the daily rates of consumption (carbon and oxygen) and the stoichiometry (O/C) were determined. In the early phase of mineralization the O/C rates increased before reaching a maximum, after which they tended to decrease. For the mineralization of leachates from C. giganteus, S. auriculata and U. breviscapa, the decrease was relatively slow. For all substrata the initial values were smaller than 1, and ranged from 0.42 (S. cubensis) to 0.81 (C. piauhyensis). The maximum values were within the range from 0.58 (U. breviscapa) to 23.1 (E. najas) and at their highest 26th (C. piauhyensis) and 106th (C. giganteus) days. These variations are believed to be associated with the chemical composition of the leachates, with their transformations and alterations of metabolic pathways involved in the mineralization.

Fipronil is a phenylpyrazole pesticide widely used to protect sugar-cane crops from insect pests. After reaching the environment, this insecticide may have several fates. This research aimed to propose a kinetic model to describe the fate of commercial fipronil Regent 800WG in the sediment-water interface of the Oleo Lagoon in the Mogi-Guaçu river floodplain, situated within the Jataí Ecological Station, by means of a microcosm scale experiment. Results showed that a small fraction of the pesticide is quickly dragged to the sediment while most of it remains in the water column. Biodegradation proves to be an important fipronil degradation route, especially when microorganisms capable of using fipronil as sole carbon source increase their population, as a function of exposure time. Biodegradation rates were higher in the sediment than in the water column.

Abstract:The Blue Peacock Bass (Cichla piquiti), native to the Tocantins-Araguaia river basin of the Amazon system, was introduced into the basin of the Paranaíba River, Paraná River system. Cachoeira Dourada reservoir is one of a series of dams on the Paranaíba River in central Brazil, where this fish has become established. A study of its feeding spectrum, combined with information about its reproductive characteristics and population structure, would enable the current state of this species in the reservoir to be assessed and might provide useful data for the management of other species native to this habitat. This study showed that the peacock bass has no predators or natural competitors in the reservoir and that reproduces continuously, with high reproductive rates, and has a smaller median length at first maturity (L50) than other species of Cichla. Its successful establishment in habitats strongly affected by human activity should cause changes in the whole structure of the local fish communities. Nonetheless, in this reservoir, there appears to be some sharing of the functions of this species with native carnivorous fish, a situation that may be sustained by the presence of a wide variety of foraging fish. Rev. Biol. Trop. 59 (2): 727-741. Epub 2011 June 01.

) medindo 5,4 cm em média, e com peso médio de 3,2 g, e seis casais de tilápia, com 12,4 cm e 32,46 g de comprimento total médio e peso total médio, respectivamente. As tilápias foram alimentadas com ração de frango farelada com 23% de proteína bruta em quantidades de 2% da biomassa inicial, durante todo o período de cultivo, apenas para manter as necessidades básicas. O crescimento do A. gigas, submetido ao forrageamento de alevinos de O. niloticus em cativeiro, foi estimada mensalmente pelos: incremento relativo em comprimento, incremento relativo em peso, curva de crescimento ajustada aos dados de comprimento, relação peso/comprimento, sendo que as curvas de crescimento em peso foram obtidas pelo método dedutivo da conjunção entre a relação peso/comprimento e a curva de crescimento em comprimento, a curva de sobrevivência da tilápia foi obtida pelo ajustamento da curva aos dados mensais das densidades e as curvas de biomassa pela conjunção entre as curvas de sobrevivência e a de crescimento em peso. Os resultados demonstraram que as tilápias devem ser oferecidas como alimento em tamanho inferior a 15 cm e densidades superiores a 36 peixes m -2 para cada 10 pirarucus durante todo o período de cultivo. A partir de 15 cm, a tilápia dificilmente é consumida pelo pirarucu, podendo ficar disponível ao piscicultor, para consumo. Abstract:Intercropping of Arapaima gigas (Pisces, Arapaimatidae) with tilapia, Oreochromis niloticus (Pisces, Cichlidae). In order to study the growth of Arapaima gigas (Pisces, Arapaimatidae) and Oreochromis niloticus (tilapia) in a mixed system, a fish pond of 190 m 2 surface area was excavated in Gleissolo Háplico soil and stocked with 10 arapaima individuals measuring an average of 21.5 cm and weighing an average of 54.21 g. The tilapia stock amounted to a total of 6840 individuals (36 individuals m -2 ), each fish measuring 5.4 cm on average with an average weight of 3,2 g, and six pairs of mature tilapia, with 12.4 cm average length and an average weight of 32.46 g. The tilapia were fed chicken feed with 23% raw protein in quantities of 2% of initial biomass throughout the growing season for the sole purpose of meeting their basic needs. Evaluation of the growth of A. gigas fed on O. niloticus minnows in captivity was estimated monthly according to several indices: weight gain relative to length, relative increase in weight, growth curve fitted to length, and weight to length. Weight was obtained from the regression between weight to length and the growth curve for length. The survival curve for tilapia was obtained by plotting monthly density data. Tilapia biomass curves were obtained from curves for survival and weight. The results showed that tilapia smaller than 15 cm in length should be offered as food at densities exceeding 36 individuals m -2 for every 10 arapaima throughout the growing season. Tilapia longer than 15 cm are almost never consumed by arapaima and may be available for fish farming for human consumption.

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