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The composition, diversity and similarity of fish communities associated with macrophytes of two oxbow lakes of Mogi-Guacu River, Sao Paulo State, Brazil, were evaluated in the wet and dry seasons of 1994–1995. Fish species composition and relative abundance values were similar for both lakes, despite their difference in connection time to the river and the abundance of macrophytes. The fish communities were predominantly composed by small sized species typical of lentic environments (Characidae), juveniles of large non-migratory species (Erythrinidae and Gymnotidae) and a few juveniles of migratory species (Anostomidae and Curimatidae). These lakes are not characterized as nurseries for the young of migratory species and the zooplankton does not have an important role as food in the ontogenetic development of migratory species of fish.

Common name: barrigudinho. Conservation status: Included in the list of threatened species in Brazil and Sao Paulo State (MMA 2004; www.ambiente.sp.gov. br/listas_fauna.zip). Identification: Lateral processes of trowel-like appendix of gonopodium large; left and right halves of trowel-like appendix of gonopodium united along its whole extension; four or more round to elliptical dark blotches along ventral half of flanks; dorsal fin densely pigmented in black. Characterized by 27–28 longitudinal series scales this species can be distinguished from its congeners by ten dorsal-fin rays (Lucinda et al. 2005). Illustration from Ihering (1930). Distribution: Endemic to Mogi-Guacu and Pardo rivers, upper Parana, Brazil (Ihering 1930; Obara and Mendes 1990; Meschiatti et al. 2000a; Ferreira 2007). Abundance: Described in 1930, it is rarely caught since then; 66 specimens reported in the literature. Habitat and ecology: Thrives among submerged vegetation in shoals (Obara and Mendes 1990); is of diurnal habits and feed on macrophytes, periphyton, drifting and superficial prey items that include, aquatic and terrestrial insects, and microcrustaceans (Obara and Mendes 1990; Meschiatti et al. 2000b). There is no information on growth and longevity. Reproduction: Males (24 mm SL) are smaller than females (30 mm SL), the gonopodium is long and with a terminal appendix. Pectoral and pelvic fins without specialization for reproduction (Rosen and Tucker 1961). The minimum sizes of mature and pregnant females are 14.5 and 16.5 mm SL, respectively. The number of embryos varies from 6 to 14, all at the same developmental stage (personal observation). Threats: The main factors affecting this species in Mogi-Guacu and Pardo rivers are sand dredging, water pollution by raw domestic and industrial sewage, pesticides and fertilizers (Meschiatti and Arcifa 2009). Conservation actions and recommendations: Areas of the Mogi-Guacu and Pardo basins are priorities for conservation, preservation, and restoration strategies for reestablishing the biodiversity of Sao Paulo State (Pesquisa Fapesp 2007). Environ Biol Fish (2009) 86:321–322 DOI 10.1007/s10641-009-9513-4