The purpose of this study was to analyze the reproductive strategy and life-history traits involved in the reproductive processes of P. mesopotamicus in two regions of the Cuiabá River basin, the first of these encompassing its headwaters (Cuiabazinho River -Rosário Oeste) and the other the flood area of the Cuiabá River (Porto Cercado -Poconé). A total of 391 individuals were sampled monthly from August 2006 to July 2007, 159 from the headwaters and 232 from the flood area. The size structure indicated that the females in the headwaters attain longer lengths than the males, while no differences in length were found in the flood area. Females predominated in the headwaters, while males outnumbered females in the flood area. The reproductive period in the headwaters extended from October to March, but was restricted to October and November in the flood area. Feeding activity showed significant differences in both sexes between the stages of gonadal maturation, with the highest values recorded in stages of gonadal inactivity. The length at first maturity was 34.89 cm and the length at which all specimens were ready for reproduction was 44 cm at both sampling sites. The spawning type was total and fecundity was positively correlated to the size of the female.O presente estudo teve como objetivo analisar a estratégia reprodutiva e os traços de história de vida relacionados aos processos reprodutivos de P. mesopotamicus em duas regiões da bacia do rio Cuiabá: uma que representa a região das cabeceiras (rio Cuiabazinho -Rosário Oeste) e outra que abrange a área de inundação do rio Cuiabá (Porto Cercado -Poconé). Indivíduos foram amostrados, mensalmente, no período de agosto de 2006 a julho de 2007. Foram amostrados 391 indivíduos, sendo 159 de ambiente de cabeceira e 232 de área alagada. A estrutura de tamanho mostrou que em ambiente de cabeceira as fêmeas atingem comprimentos maiores que os machos, enquanto que em área alagada não houve diferença nos comprimentos. Ocorreu predomínio de fêmeas em ambiente de cabeceira, e de machos em área alagada. O período reprodutivo para o ambiente de cabeceira estendeu-se de outubro a março e para a área alagada foi restrito a outubro e novembro. A atividade alimentar apresentou diferenças significativas para ambos os sexos entre os estádios de maturação gonadal com os maiores valores encontrados em estádios de inatividade gonadal. O comprimento de primeira maturação foi de 34,89 cm e o comprimento em que todos estão aptos a reproduzirem foi de 44 cm para ambos os locais. O tipo de desova é total e a fecundidade foi positivamente relacionada ao tamanho da fêmea.

Growth is a fundamental biological process, driven by multiple endogenous (intra-individual) and exogenous (environmental) factors that maintain individual fitness and population stability. The current study aims to assess whether individual, spatial (headwaters and floodplains) and inter-sex variation occurs in the growth of Piaractus mesopotamicus in the Cuiabá River basin. Samples were collected monthly from July 2006 to July 2007, at two areas in the Cuiabá River basin (headwaters and floodplain). Three growth models (individuals; individuals and sex factors; individuals and areas factors) were developed and compared the fish growth parameters using Akaike information criterion (AIC). The best fit to the length-at-age data was obtained by a model that considered individual variation and sex. The theoretical maximum average length (L ∞ ) was 64.99 cm for females, and 63.23 cm for males. Females showed a growth rate (k) of 0.230 yr -1 and males of 0.196 yr -1 . Thus, could be concluded that individual variability and sex were the main sources of variation in P. mesopotamicus somatic growth parameters.Keywords: Age, Growth models, Inter-sex variation, Otoliths, Von Bertalanffy O crescimento é um processo biológico fundamental, impulsionado por múltiplos fatores endógenos (intra-individual) e exógenos (ambientais) que mantém o fitness individual e a estabilidade populacional. Este trabalho tem como objetivo avaliar se ocorre variação individual, espacial (região de cabeceira e planície de inundação) e entre sexo no crescimento de Piaractus mesopotamicus na bacia do rio Cuiabá. Amostragens foram realizadas mensalmente entre julho de 2006 a julho de 2007, em duas áreas da bacia do rio Cuiabá (região de cabeceira e planície de inundação). Três modelos de crescimento (indivíduos, indivíduos e sexo como fator, indivíduos e área como fator) foram elaborados e comparados os parâmetros de crescimentos dos peixes com base no critério de Informação de Akaike (AIC). O melhor ajuste aos dados de comprimento na idade data foi obtido pelo modelo que considerou a variação individual e o sexo. O comprimento médio máximo teórico (L ∞ ) das fêmeas foi 64,99 cm e para os machos 63,23 cm. O coeficiente de crescimento (k) médio foi de 0,230 yr -1 e 0,196 yr -1 , respectivamente para fêmeas e machos. Portanto, pode-se concluir que variabilidade individual e sexo foram as principais origem de variação dos parâmetros de crescimento somático de P. mesopotamicus. Palavras-chave:Dimorfismo sexual, Idade, Modelos de crescimento, Otólitos,

Using morphometric measurements and wavelets functions, the asterisci otoliths of curimatã, Prochilodus nigricans were analysed to identify the variation in shape and growth increment of individuals from Solimões, Japurá and Negro rivers of the Amazon basin, Brazil. The morphometric and morphological analyses did not reveal evidences of population segregation among rivers, but variations were found in the estimation of otolith growth increment. Also, the otolith shape showed a high variability between individuals, identifying four morphotypes. Morphotype 1 shows a more oval shape with a posterior zone clearly rounded; Morphotype 2 shows the posterior zone rounded, but the anterior end is more elongated; Morphotype 3 shows a completely different shape, elliptic-pentagonal and Morphotype 4 shows the posterior zone rounded, but the anterior end is more elongated and it is the pattern with antirostrum and rostrum more pointed and a deep notch. Therefore, the otolith shape exhibited a phenotypic plasticity that it was not associated with the metabolism of otolith growth. Whereas the otolith shape indicated a homogeneity in the sound perception through Amazon basin, the growth rates revealed an adaptive mechanism to environmental conditions or migratory process of this species.

Aquatic organisms that consume resources from riparian vegetation or floodplain forests act as trophic links between aquatic and terrestrial ecosystems. For instance, the pacu Piaractus mesopotamicus (Holmberg 1887), which is a migratory fish species, can play an important role in this interaction on Neotropical floodplains. We compared the stomach content of individuals from this species between two different parts of a large river floodplain during contrasting hydrological seasons to quantify the spatiotemporal contribution of allochthonous and autochthonous resources in their diet. Moreover, we performed a bipartite network approach to evaluate the sensitivity of these populations to a simulated loss of food resources through the potential deforestation of riparian vegetation. We found that in the upper catchment, individuals fed mainly on allochthonous items, but their identity depended on the season: fruits were the most abundant resource during the wet season, whereas leaves were more consumed during the dry season. In the lower catchment, the contribution of allochthonous resources was slightly lower in the dry season than in the wet season, when the pacu was able to explore the floodplain. Finally, the results from our consumer-resource network model indicated that this system is vulnerable to riparian deforestation since P. mesopotamicus is highly dependent on input from the riparian vegetation items to its feed.