Botânica e Ecologia

A ecologia reprodutiva de Moenkhausia sanctaefilomenae (Steindachner, 1907) foi estudada em 15 lagoas da planície de inundação do rio Cuiabá, Mato Grosso. Foram analisadas a proporção sexual, a época de maturação, tipo de desova e o comprimento de primeira maturação. Foram amostrados 212 indivíduos (108 fêmeas e 104 machos) no período de junho de 2005 a março de 2006. Não houve diferença significativa na proporção sexual, considerando todo o período amostrado. A maior freqüência de fêmeas maturas foi encontrada em dezembro em todas as lagoas. A largura média dos folículos ovarianos variou entre os períodos, sendo que em dezembro estes foram em média maiores. Sugerindo que a desova ocorreu, provavelmente, entre o final de dezembro e início de janeiro, o que corresponde aos períodos de enchente e cheia na região. A observação de um padrão polimodal da distribuição de freqüência de largura dos folículos ovarianos sugere desova parcelada, mas restrita ao período de dezembro a março. O c...

Os parâmetros de crescimento e mortalidade estimados a partir da estrutura em comprimento foram utilizados para avaliar o estado de explotação dos estoques de quatro espécies de grandes bagres da bacia do rio Cuiabá, Pantanal norte. As espécies estudadas foram o barbado, o cachara, o jaú e o pintado. As avaliações foram realizadas por meio do modelo de rendimento por recruta, considerando os Pontos de Referência Biológicos Fmax, F0,1, F = M e F BDR. As análises indicam que os estoques do pintado e do jaú estão bem conservados. Os estoques do cachara e, menos fortemente, o do barbado estão em iminente ameaça de sobrepesca na bacia do rio Cuiabá.

ABSTRACT Density-dependent regulation is a necessary process for the long-term persistence of populations. Nevertheless, ecologists still debate whether floodplain fish populations are subject to density-dependent dynamics or mostly regulated by the density-independent seasonal flooding. We surveyed Jewel tetra (Hyphessonbrycon eques) populations during 4 years in the floodplain lagoons of the Cuiabá River (Brazil) in order to determine if recruitment, growth, and survival are subject to density-dependent effects. We showed that population dynamics of this species are influenced by the seasonal drought, which affects the various life stages of the cohort in different ways. The flood had positive effects on the strength of recruitment, and indirectly affected the probability of survival of recruits during the following dry season as well as on the extinction probability of local populations. Additionally, by facilitating the dispersal of pre-larvae and juvenile recruits, it enables the re-establishment of locally extinct populations during the preceding dry season. Therefore, flooding is essential for the persistence of the species at the regional scale. On the other hand, the limiting conditions during the dry season cause high mortality rates among juveniles. More importantly, the mortality during the dry season is density-dependent and causes changes in population size structure and extinction of local populations, which will affect recruitment in the following year. Our results change the traditional belief that flood alone control population dynamics of fish dwelling in floodplains of larger rivers but a longer survey is required to better understand the effects of drought.

ABSTRACT Freshwater habitats are among the most impacted ecosystem on Earth. Consequently, reserves have been implemented in an attempt to reduce the threat to freshwater biodiversity. However, few studies have evaluated how effective these protected areas (PA) are for the conservation of freshwater organisms. In the present study, we compared species richness, community composition and density of small-bodied fishes between lagoons within an eight-year-old reserve (i.e. protected lagoons) with those outside the reserve (i.e. unprotected lagoons) in a river-floodplain system that is exposed to seasonal flooding. The unprotected lagoons have been submitted to a light fishing pressure mainly targeting small-sized fishes for sale as baits. Our results showed no differences between the lagoons inside the reserve with those outside in any of the community properties measured. However, we registered an overall tendency of abundance reduction among the species used as baits in unprotected lagoons. Considering the high degree of oversight in the PA and the low fishing pressure among unprotected lagoons, it is possible that the positive effects promoted by the reserve on fish assemblages are being exported towards unprotected lagoons and thus offsetting a portion of the anthropogenic impacts. We conclude that the protection provided by the reserve is very efficient in river-floodplain systems, because not only it protects the biota inside the reserve but also act as a source of propagules to unprotected areas during the rainy season when all the aquatic subsystems are connected by the flood.

Researches on ichthyoplankton seems to be an important tool to identification of spawning areas and periods for freshwater fish. Ichthyoplankton was sampled monthly in the headwaters of the Cuiabá River, upper Paraguay River basin, (Mato Grosso State, Brazil), and in four of its tributaries, between November 2007 and March 2008, to evaluate the spatial and temporal distribution of fish eggs and larvae and the influence of regional and local variables on their distribution. In total, 22,067 eggs and 1,045 larvae were collected. A significant negative correlation was found between egg density and the variables of river level and flow volume. Larval density was not significantly correlated with any of the regional variables. The egg and larval densities were significantly higher at the sampling sites in the main river. The highest densities were found in environments with greater river widths, intermediate depths and lowest values of dissolved oxygen, electrical conductivity, and trans...

The comprehension of the reproductive cycle allows to understand which are the morphological changes that develop in the gonad during this interval. Thus, many studies have been undertaken in order to describe and classify the stages of gonadal development and reproductive status of Neotropical fishes. For this purpose, specimens of Melanorivulus aff. punctatus were collected in a permanent dam in Chapada dos Guimarães, Mato Grosso, Brazil. The gonads were prepared for analysis by light microscopy. The oogenesis and spermatogenesis have been described, characterizing the stages of gonadal development, together with assessments of the gonadosomatic ratio, germ cell count and verification of variation of mature oocytes in females. Throughout the year the male gonads presented themselves as capable of reproducing, characterized by the presence of undifferentiated and differentiated spermatogonia, spermatocytes organized into cysts, spermatids in cysts whose wall was thicker and the spe...

The study of the reproductive biology of Triportheus trifurcatus of the middle rio Araguaia was carried out using 275 specimens obtained in seven collections conducted in the period between November 2003 and January 2005. Females prevailed among the classes of intermediate length, as well as in the total number of samples. On the other hand, males prevailed in the smaller classes. The average length of females was larger than that of males. Four stages of gonadal maturation were macro- and microscopically identified: B - maturation, C - mature, D - spent and E - resting. Stage A (immature) was not found in the habitats sampled. The smallest-length male was 110 mm in standard length, and the smallest female, 119 mm. The spawning period occurred from November to January, with reproductive peak in December/January, coinciding with the highest water levels. The absolute fecundity is considered low, and there is a positive correlation between fecundity and gonad weight, body weight and s...

Resumo Ácaros do gênero Otodectes são parasitos encontrados frequentemente no ouvido de cães e gatos, sendo reconhecidos como os principais causadores de otite externa nesses animais. Trezentos e vinte cães, oriundos do município de Cuiabá, Mato Grosso, foram examinados através da otoscopia e do exame do swab parasitológico, com o objetivo de avaliar, através da análise bayesiana para a estimativa da prevalência, sensibilidade e especificidade destes métodos no diagnóstico da infestação causada pelo ácaro utilizando-se de dados a priori informativos e não informativos. Cada animal foi considerado uma unidade experimental. Do total de cães examinados, 142 (44,37%) apresentaram-se positivos para otocariose. Em 100 animais (31,25%) a infestação foi diagnosticada pelos dois métodos, em 31 (9,69%) apenas pelo exame do swab parasitológico, em 11 (3,44%) apenas pela otoscopia e em 178 (55,62%) animais o resultado foi negativo por ambos os métodos. A sensibilidade da otoscopia, quando compa...