Abstract The present study aims to describe the population structure of the freshwater prawn Macrobrachium brasiliense and to analyze whether it varies seasonally, with emphasis on abundance variation by demographic category, sex ratio, size, and morphotypes, in addition to analyzing the recruitment period and its relationship with rainfall. The collections of M. brasiliense were carried out in a Cerrado region, in the southeastern region of Brazil. The population structure was analyzed according to the size, sex, and life stage. The density of morphotypes was calculated by the proportion of each morphotype in the population. Male and female prawns were more abundant in the largest and smallest size classes, respectively. The juvenile morphotype was the most abundant among males (45.9 %), while the “Mirim” and “Açu” morphotypes occurred in a similar proportion (27.87 % and 26.23 %, respectively). The population structure varied significantly between seasons (dry and rainy). A relationship of juvenile abundance with rainfall was recorded. The recruitment period was observed between the end of the rainy season and the beginning of the dry season, while adults were more abundant at the end of the dry season and the beginning of the rainy season. The information in this study contributes to the knowledge of the influence of seasonality and rainfall on populations of aquatic organisms in the Cerrado region, such as the prawn M. brasiliense. Rainfall seasonality affects the population structure of these organisms between seasons, possibly due to the top-down and bottom-up effects caused by different rates of nutrient input in such aquatic systems.

RESUMO O objetivo principal deste estudo foi estimar a maturidade sexual morfológica de Macrobrachium brasiliense (Heller, 1862) e analisar o crescimento relativo da espécie. Durante um ano de coleta, de julho de 2012 a junho de 2013, foram coletados 199 espécimes em um riacho localizado em um bioma de Cerrado, na região do Triângulo Mineiro. Uma vez identificados e sexados, procedeu-se as medições (mm) do comprimento da carapaça, comprimento dos artículos do segundo pereópode (ísquio, mero, carpo, própodo e dáctilo) e largura da pleura. Os tamanhos máximos e médios do comprimento da carapaça foram 20,5 (média: 9,6 ± 4,2 mm) e 20,1 mm (média: 7,7 ± 3,4 mm) em machos e fêmeas, respectivamente. O comprimento do própodo para machos, e a largura da pleura para fêmeas foram utilizados para a classificação dos individuos em juvenis e adultos, usando a análise de K-means e análises discriminantes. O crescimento relativo das espécies também foi avaliado através da análise de covariância para todas as estruturas (ANCOVA, α = 0,05). Nas fêmeas, o crescimento da maioria das estruturas ocorreu igualmente entre juvenis e adultos, com exceção do mero e pleura. Por outro lado, o crescimento de quase todas as estruturas dos machos diferiu entre juvenis e adultos. Apenas o crescimento do carpo e da pleura foi semelhante. O tamanho no início da maturidade sexual morfológica foi estimado em 8,64 mm CL para machos (CL50% r = 1,71) e 8,03 mm CL para fêmeas (CL50% r = 0,07). Os resultados obtidos contribuem para a compreensão de algumas questões importantes relacionadas à biologia reprodutiva de M. brasiliense. Foi possível notar que os machos apresentam um crescimento diferencial quando comparados às fêmeas e se tornam os maiores indivíduos da população, resultando em um dimorfismo sexual. Tal dimorfismo sexual pode promover o desenvolvimento do comportamento de guarda temporária de acasalamento, uma estratégia reprodutiva muito importante para alguns camarões carídeos.

ABSTRACT The main objective of this study was to estimate the morphological sexual maturity of Macrobrachium brasiliense (Heller, 1862) and to analyze the relative growth of the species. During one year of sampling, from July 2012 to June 2013, 199 specimens were collected in a stream located in a Cerrado biome, in the Triângulo Mineiro region, state of Minas Gerais. Once identified and sexed, the length of the carapace, the length of the segments of the chelipeds (ischium, merus, carpus, propodus and dactyl) and width of the pleura were measured (mm). The maximum and mean sizes of the carapace length measured 20.5 mm (Mean: 9.6 ± 4.2 mm) and 20.1 mm (Mean: 7.7 ± 3.4 mm) for males and females, respectively. The propodus length for males, and the pleura width for females, were used for the classification of the specimens into juvenile and adult, using K-means analysis and discriminant analysis. The relative growth of the species was also evaluated through covariance analysis for all structures (ANCOVA, α = 0.05). In females, the growth of most structures occurred equally between juveniles and adults, with the exception of the merus and pleura structures. On the other hand, the growth of almost all structures of males differed between juveniles and adults. Only the carpus and the pleura growth were similar. We also estimated the size at onset of morphological sexual maturity at 8.64 mm CL for males (CL50% r = 1.71) and 8.03 mm CL for females (CL50% r = 0.07). Our results contribute to the understanding of some important questions related to the reproductive biology of M. brasiliense. We noted that males grow differently from females and become the largest individuals in the population, resulting in a sexual dimorphism. Such sexual dimorphism might promote the development of the temporary mating guarding behavior, a reproductive strategy very important for caridean shrimps.

Abstract The goal of this study was to evaluate the reproductive investment (RI) and the fecundity of the shrimp Nematopalaemon schmitti (Holthuis, 1950), caught by trawling in the southeastern Brazilian coast in 2008, 2009 and 2011. The carapace length (CL) of ovigerous females was measured and the development stage of their ovaries and embryos were analyzed. A significant relationship was observed between the female body and embryo weights (Linear regression: r² = 0.26, F = 20.77, P < 0.0001, Ln BDW = 0.92. Ln FBDW - 2.24) and between number of embryos and CL (Linear regression; stage I: r² = 0.38, F = 36.15, P < 0.0001; stage II: r² = 0.34, F = 14.10, P < 0.001), but not between the RI and CL (ANOVA: F = 0.47, df = 7, P = 0.85). Association of the changes in embryo development and ovarian maturation of ovigerous females was tested. Females with rudimentary ovaries predominantly showed embryos in stage I (early development) and females with developed ovaries only showed embryos in stage II (final development), showing synchrony between the development of both, thus supporting the hypothesis of a continuous reproductive cycle for N. schmitti in the region. Such information is fundamental for understanding the reproductive biology of these crustaceans, as well as other caridean shrimps, in order to promote the maintenance and preservation of natural stocks.

ABSTRACT We analyzed the spatio-temporal variations of the abundance, distribution and the population structure of Hexapanopeus paulensis Rathbun, 1930 from the southeastern Brazilian coast. Monthly samples were taken from January 1998 to December 1999 at Ubatumirim, Ubatuba and Mar Virado bays. A total of 1084 individuals were obtained, 76 specimens at Mar Virado, 322 at Ubatuba and 686 at Ubatumirim. It was possible to verify an association between the abundance of H. paulensis and bottom temperature (positive correlation), grain size of sediment and organic matter content (both negatively). This explains the higher number of individuals in the stations nearest to the continent (with higher temperature values and heterogeneous substrate). Juveniles were recorded throughout the study period, constituting 39.5% of the sampled population, which highlights the importance of the region (especially Ubatumirim Bay, due the highest abundance) for the establishment of the species. Only females occupied the largest size classes, which could mean differential mortality between the sexes or growth rate. Nevertheless, further studies should be accomplished to a better comprehension of such difference.

In this study, we estimated the size at onset of maturity (carapace width, CW50) and analyzed the relative growth of some body parts and the heterochely of the mud crab Hexapanopeus paulensis. A total of 800 crabs were collected, from January 1998 to December 1999, on the southeastern coast of Brazil. Each specimen was sexed and measured. CW50 was estimated to be 6.7 mm in males and 6.3 mm in females. Carapace length growth was negatively allometric in both sexes. Cheliped length and height was positively allometric for both males and females. Gonopod growth was isometric (b = 1) and negatively allometric (b < 1) in both juvenile and adult males, respectively. Abdomen relative growth was positively allometric (b > 1) for both juvenile and adult females. In males and females, the right cheliped was larger and higher than the left cheliped. Such heterochely may be related to the feeding habits of H. paulensis. Most xanthoid crabs, including the studied species, feed upon mollusks with dextral shells, which require complicated handling. In this sense, the heterochely in H. paulensis might facilitate the food manipulation.

En esto estudio se investigó la talla de primera madurez sexual (ancho del caparazón CW50), crecimiento relativo de varias estructuras corporales y la ocurrencia de heteroquelia en machos y hembras de Hexapanopeus paulensis. Se recolectó un total de 800 ejemplares, de enero 1998 diciembre 1999 en la región de Ubatuba, costa sureste de Brasil. Cada cangrejo recolectado fue sexado y medido. El CW50 ocurre a los 6,7 mm en machos y 6,3 mm en hembras. En machos juveniles y adultos, el crecimiento relativo (basado en el CW) del gonopodio fue isométrico (b = 1) y alométrico negativo (b < 1), respectivamente. El crecimiento relativo del abdomen fue alométrico positivo (b > 1) en hembras juveniles y adultas. El crecimiento relativo del ancho del caparazón fue alométrico negativo en los dos sexos. El alto y largo del quelípedo presentaron alometria positiva. El quelípedo derecho (largo y alto) fue más grande que el quelípedo izquierdo tanto en los machos como hembras. Consecuentemente, H. paulensis exhibe heteroquelia, lo que sugiere especialización de los quelípedos en relación a su hábito alimentario. Tanto H. paulensis como otros cangrejos xantoideos se alimentan de moluscos con conchas dextrógiras, y la destrucción de dichas conchas requiere de un manejo complejo de sus quelípedos. De este modo, los quelípedos heteroquélicos pueden facilitar la manipulación del alimento en el cangrejo H. paulensis.

OBJETIVO: A biologia populacional do camarão de água doce Macrobrachium jelskii foi investigada, com ênfase na distribuição de frequência em classes de tamanho, razão sexual, período reprodutivo e recrutamento juvenil. Além disso, a abundância dos indivíduos foi correlacionada com os fatores abióticos. MÉTODOS: Amostras foram coletadas mensalmente de julho de 2005 a junho de 2007, às margens do Rio Grande, região de Planura, estado de Minas Gerais, Brasil (20º 09' S e 48º 40' W), usando uma rede de arrasto (1.0 mm tamanho da malha e 2.0 × 0.5 m de largura). O equipamento foi arrastado por duas pessoas às margens da vegetação do rio por 100 metros de distância, percorridos por uma hora. Em laboratório, os espécimes foram identificados, mensurados e sexados. RESULTADOS: Um total de 2,789 espécimes foi analisado, no qual correspondem a 1,126 machos (549 jovens e 577 adultos) e 1,663 fêmeas (1,093 jovens, 423 adultos não ovígeras e 147 ovígeras). A razão sexual diferiu significativamente a favor de fêmeas de M. jelskii (1:1.48; χ² = 103.95; p < 0.0001). A média de tamanho do comprimento da carapaça (CL) das fêmeas (6.32 ± 1.84 mm CL) foi estatisticamente maior do que dos machos (5.50 ± 1.07 mm CL) (p < 0.001). A distribuição de freqüência em classes de tamanho dos espécimes revela um padrão de distribuição unimodal e não normal para machos e fêmeas (W = 0.945; p < 0.01). Não foi observada relação entre a abundância de M. jelskii e as variáveis ambientais (p = 0.799). CONCLUSÃO: A presença de fêmeas ovígeras e jovens na população sugere um padrão de reprodução e recrutamento contínuos para M. jelskii na região de Planura.

AIM: The population biology of the freshwater shrimp Macrobrachium jelskii was investigated here emphasizing the length-frequency distribution, sex ratio, reproductive period and juvenile recruitment. In addition, the abundance of individuals was correlated with the abiotic factors. METHODS: Samples were collected on a monthly basis from July 2005 to June 2007 along the river margin in shallow water of Grande River, at Planura region, State of Minas Gerais, Brazil (20º 09' S and 48º 40' W), using a trawl net (1.0 mm mesh size, and 2.0 m × 0.5 m wide). The fishing gear was handled by two people along the marginal vegetation of the Grande River in a course of 100 m, covered for one hour. In the laboratory, the specimens were identified, measured and sexed. RESULTS: A total of 2,789 specimens was analyzed, which corresponded to 1,126 males (549 juveniles and 577 adults) and 1,663 females (1,093 juveniles, 423 adults non-ovigerous and 147 ovigerous). The sex ratio differed significantly in favor of the females of M. jelskii (1:1.48; χ² = 103.95; p < 0.0001). The mean size of carapace length (CL) of females (6.32 ± 1.84 mm CL) was statistically higher than of males (5.50 ± 1.07 mm CL) (p < 0.001). The length-frequency distribution of the specimens revealed an unimodal pattern and non-normal distribution for males and females (W = 0.945; p < 0.01). No significant relationship between the abundance of M. jelskii and the environmental variables was observed (p = 0.799). CONCLUSION: The presence of ovigerous females and juveniles in the population suggests a continuous reproduction pattern and recruitment for M. jelskii at Planura region.