Abstract:In order to describe some aspects of the population ecology of Bryconamericus stramineus in the Guiraí River basin, upper Paraná River basin, samples were taken bimonthly from October 2006 to August 2007 at seven sites in the basin. A total of 960 individuals, including 532 females, 316 males, and 112 of undetermined sex, were collected. A significant variation in the sex ratio was observed (χ 2 = 32.82; p < 0.001). Females were larger (59.7 mm) than males (58.9 mm); however, males showed a larger angular growth coefficient (b) than females. It was estimated that 50% of females were sexually mature at 36.4 mm. The highest rate of ovary development was observed in October, while in June 2007 no mature females were found. Mean fecundity was estimated at 313 eggs, and the relative fecundity was 184.6 eggs/g. The asymptotic was estimated at 62.8 mm and the growth rate at 0.76. The growth performance index was calculated at 3.47, the longevity at 3.94 years and the mortality (M) at 1.18 years. The recruitment pattern of the species showed peaks concentrated in periods of low rainfall. Keywords: length-weight relationship, mortality, reproductive strategy, sex ratio. Neotrop., vol. 11, no. 2 In which season does reproductive activity of B. stramineus increase in the streams sampled? 5) What is the mean standard length at which females reach first maturation? 6) Is there any relationship between fecundity and the size of females? 7) Are seasonal differences in recruitment patterns for studied population? 8) What are the growth and mortality parameters for B. stramineus in sampled streams?
Material and Methods
Study siteThe Guiraí River basin (22° 45' S, 54° 30' W and 22° 15' S, 53° 30' W), occupies an area of approximately 2,248 km 2 and includes seven municipal districts. The mouth of the Guiraí River is located at an altitude of 370 m a.s.1., and the river flows for approximately 100 km until it enters the Ivinhema River, at 238 m of altitude. In its lower portion, it forms the boundary of the Parque Estadual das Várzeas do rio Ivinhema.
Field and laboratory methodsThe fish samples were taken bimonthly from October 2006 to August 2007 at seven sites in the Guiraí River basin (Figure 1). The streams were selected for their location in the basin and ease of access.The samples were taken during daylight, with a rectangular sieve measuring 1.2 × 0.8 m (2 mm mesh size) and standardized effort (20 throws) at each site, with approximately 100-m long hauls. The equipment was slide to sweep the substrate toward the banks of the stream. This technique was used because of the difficulties of using the electric fishing in these streams, such as low electrical conductivity and high turbidity, and also due to difficult access. The permission for fish retrieval was granted by IBAMA (#13458-1).Specimens were fixed in 10% formalin and preserved in 70% ethanol for subsequent identification. Voucher specimens were deposited at the Coleção de Peixes do Nupelia (NUP/UEM # 9322).In the laboratory, some biometric data were mea...