Reproductive biology of Hyphessobrycon eques (Characiformes: Characidae) in Southern Pantanal, Brazil

Abstract Population and reproductive aspects allow the knowledge and understanding of population dynamics and the influence of environmental factors, in addition to ensure the success of a species continuity. Thus, the aim of this study was to analyze population and reproductive traits of the species Hyphessobrycon eques in southern Pantanal, Brazil. Monthly samplings were conducted from February/2009 to January/2011, with 617 individuals analyzed, being 365 females and 262 males. A similar form of distribution in length and weight between the sexes was observed. There was no significant variation in sex ratio over time, with higher proportion of females during the entire sampled period. Both sexes presented a angular coefficient of Weight/Length (b) relationship greater than 3, with speed of increase in weight greater than in length. For females, a long reproductive period was observed, with greater reproductive intensity from January through June. No significant correlation was observed between the Gonadosomatic Index (GSI) and the average temperature, rainfall and river level, despite the fact that reproductive activity occurs in autumn/winter, when there are favorable conditions due to flooding. The size at first maturation (L50) was 20.2 mm, with confidence interval varying from 19.7 through 20.7 mm. The average fecundity was 191.9 oocytes/females and was significantly related to the standard length and total weight (g), demonstrating a relation with energy accumulation to invest in reproduction. The long reproductive period, intensified by partial spawning, higher proportion of females and low L50, show that the species has strategies necessary for survival and rapid population growth, common in small species characterized as r-strategists

REGIME TÉRMICO EM ÁGUAS CORRENTES E SUA IMPORTÂNCIA NA ESTRUTURA DO HABITAT E NA BIOLOGIA DE ORGANISMOS AQUÁTICOS

O regime térmico em águas correntes e os processos responsáveis por sua variabilidade, são de grande importância ecológica. Uma vez que a temperatura da água influencia a distribuição, reprodução, crescimento e desenvolvimento dos organismos aquáticos, além de produzir efeitos sobre o metabolismo ecossistêmico. Nesta perspectiva, este trabalho revisou os aspectos relevantes à variabilidade térmica de águas correntes, os fatores que os influenciam e sua importância na estrutura do habitat e na biologia de organismos aquáticos. Com este propósito, observou-se que flutuações na temperatura da água podem ocorrer naturalmente devido às condições atmosféricas, topografia, descarga e condições do leito ou por perturbações antrópicas, tais como, represamento, desmatamento e mudanças climáticas. A heterogeneidade térmica ocorre desde escalas locais em gradientes verticais de temperatura da coluna de água, bem como em escalas regionais ao longo do gradiente longitudinal. Flutuações temporais da temperatura também são evidentes e ocorrem diariamente (hora do dia) e sazonalmente (estações do ano). Tanto espacial quanto temporalmente, a estabilidade (ou variabilidade) da temperatura depende da descarga do rio. A temperatura da água influi diretamente nas condições do habitat provocando alterações nas reações químicas, reduzindo as concentrações de oxigênio na água, formando barreiras térmicas, entre outros efeitos. Tais condições podem causar elevação da taxa de crescimento de plantas aquáticas, desequilíbrio no período de eclosão de ovos (principalmente de peixes), aumento à suscetibilidade a doenças, alterando, desta forma, o funcionamento do ecossistema. Portanto, torna-se evidente a importância da temperatura da água como fator relevante no controle ambiental de águas superficiais

Spatial distribution of fish assemblages along environmental gradients in the temporary ponds of Northern Pantanal, Brazil

Ten temporary ponds in northern Pantanal were studied in July 2006 to explore whether a spatial distribution pattern existed in the composition of fish assemblages, and to identify which environmental variables determined their distribution. The existence of any spatial pattern was tested using the multivariate Mantel correlogram, while the influence of environmental variables was quantified by a Canonical Correspondence Analysis (CCA). A total of 8735 individuals was sampled from 29 species, predominantly represented by <em>Hyphessobrycon elachys</em> and <em>Serrapinnus calliuru</em>s. Composition of fish assemblages varied among ponds, but this variation had no significant spatial pattern for any of the distance classes considered, thus indicating that the species composition varied independently of the distance between ponds. This suggests that stochastic dispersal processes did not influence the spatial structure of species, as predicted by the neutral theory. Conversely, species composition in the ponds was determined by variables that included depth, macrophyte richness and cover. Species such as <em>Markiana nigripinnis</em>, <em>Crenicichla vittata</em> and <em>Moenkhausia sanctaefilomenae</em> occurred in deeper waters, while <em>Parauchenipterus striatulus</em>, <em>Eigenmannia trilineata</em> and P<em>sellogrammus kennedyi</em> were mainly associated with greater richness and macrophyte cover, as already demonstrated by the niche theory applied in ponds which tended to have similar characteristics and a similar fish composition