POPULATION ASPECTS AND RECRUITMENT OF Odontostilbe paraguayensis (CHARACIFORMES: CHARACIDAE) IN THE PARAGUAY RIVER, PANTANAL, BRAZIL

Abstract

Population dynamics allows comprehension on how population assures its success on continuity of the species and the balance of its population density. Thus, in order to analyze reproductive parameters (i.e., gonadal maturation stages, fecundity, and recruitment) and population aspects (i.e., length-weight frequency, asymptotic length, growth and mortality rates, and sex ratio) of Odontostilbe paraguayensis Eigenmann & Kennedy (1903) (Characiformes: Characidae) in the southern Pantanal of Brazil, samples were carried out from February 2009 to January 2011 along the main channel of the Paraguay River and its tributary, the Amonguija River, with seine net and a rectangular sieve (0.8 x 1.2 m). To estimate population parameters, the data of 604 individuals were recorded, and for reproductive aspects, the data of 394 individuals were recorded. The sex ratio was 3:1 (females:males). The estimated asymptotic length (L∞) was 36.67 mm. The population had high growth rate values (k = 1.3 year-1) and mortality (Z = 1.98). Longevity was estimated as 2.3 years. The mean absolute fecundity was 420.2 oocytes/female. Absolute fecundity was positively related to total weight (g) and gonad weight (mg). For females, the standard length at first maturity (L50) was 24.1 mm, and for males, it was 27.6 mm. Reproducing females were more frequent in March and April, although females with ripe gonads were recorded nearly all year long. The recruitment pattern was long with positive correlation with the average historic level of the Paraguay River, considering seasonal flooding. The lengthweight relationships were not different between the sexes, but they presented negative allometric growth. Thus, during ontogeny, the species presents more increment in length than in weight, and, consistent with the high growth rate, this may be understood as a way to reach longer lengths faster to avoid predation. The outcomes demonstrate that O. paraguayensis has a short life cycle with high growth and mortality rates. Together with the long recruitment pattern and high fecundity, the species may be considered an r-strategist.