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The present study aims to propose a methodology for establishing water quality indexes which is based on the application of multivariate statistics, to be used within the limitations of the qualitative variables established by the existing legislation in any country. Data sets used were obtained from two water quality monitoring points in a spring located in the Mirim-São Gonçalo watershed, class II, which is located in the state of Rio Grande do Sul, Brazil. Factorial Analysis was used to define the qualitative variables and their respective weights in each source, whereas the Principal Component Analysis was used to extract the factors. For the construction of the water quality boundaries of classes, CONAMA Resolution 357/2005 was used for class II freshwater sources, along with reference values obtained from the literature. The new proposed water quality index WQI was compared to the WQI suggested by the Environmental Company of the State of São Paulo—CETESB (WQICETESB) to verify the similarities or disparities between them. The results indicate that the index used by CETESB is not adequate for the reality of this watershed, considering that it does not represent the reality of the water quality of the water bodies. Furthermore, this index does not include all the important variables, besides presenting weights for the variables with distorted values. It is therefore concluded that the proposed methodology for constructing water quality indexes is of significant value for the qualitative management of water resources. [ABSTRACT FROM AUTHOR]

The La Plata croaker (Pachyurus bonariensis) family Sciaenidae, is a small (< 23 cm) benthopelagic fish that originated in the Paraná- Paraguay-Uruguay river systems in South America. Its first record in the Patos Lagoon drainage area, Rio Grande do Sul (Brazil) occurred in 2001. This research reports for the first time, the occurrence of both juvenile and adult specimens of P. bonariensis in the São Gonçalo Channel (a 75 km long waterway between Patos and Mirim lagoon) and in the Mirim Lagoon, in 2005 and 2007 respectively. A total of 434 gonads were analyzed histologically from specimens captured by artisanal fishermen at Capilha, Mirim Lagoon between 2008 and 2010. Gonadal development was observed and described. Pachyurus bonariensis probably dispersed from northern Patos Lagoon in 2001 to the São Gonçalo Channel by 2005. The occurrence of adults in limnic waters in the São Gonçalo Channel and further south in the Mirim Lagoon in 2007, confirm that P. bonariensis is now an established species in Mirim Lagoon and could become a commercially important species to the artisanal fishermen of the area. Likewise at the limnetic northern parts of Patos Lagoon, P. bonariensis is now abundant at Mirin Lagoon and the ecological impacts of this range extension must be investigated. [ABSTRACT FROM AUTHOR]