Lúcia Aparecida de Fátima Mateus

Fishing resources in the rio Cuiabá basin, Pantanal do Mato Grosso, Brazil

The rio Cuiaba is one of the most important tributaries of the upper rio Paraguay basin that form the Pantanal wetlands. The fishing resources of the rio Cuiaba basin were studied based on landing data obtained from the Fish Market of the city of Cuiaba, State of Mato grosso, Brazil. A description is given of the composition and origin of the 2000 and 2001 catch. The rio Cuiaba is the main source of fish for Cuiaba, although some fish sold locally comes from the rio Paraguay. The 2000-2001 catch consisted mainly of migratory species. The main landed species were the pimelodids pintado -Pseudoplatystoma corruscans, cachara -Pseudoplatystoma fasciatum, and jau -Paulicea luetkeni, and the characiforms pacu -Piaractus mesopotamicus, piraputanga -Brycon microlepis, piavucu -Leporinus macrocephalus, and dourado -Salminus brasiliensis. Large catfishes (Pimelodidae) represented 70% of the landed fish, among which pintado was the most abundant. The data indicate that current catches are smaller than those recorded in the early 1980s and fish are caught far off the urban zone. Moreover, although the number and composition of species caught were similar to those of the 80s, the distribution of species abundance has changed. Currently, fisheries catch more carnivorous species than fish from lower trophic levels. These findings cannot be credited solely to overfishing, but appear to result from a complex interaction of factors, i.e., environmental degradation, changes in market preferences, and restrictive legal fishing regulations.

Sincronia na reprodução de Moenkhausia sanctaefilomenae (Steindachner) (Characiformes: Characidae) na planície de inundação do rio Cuiabá, Pantanal Mato-grossense, Brasil

The reproductive ecology of Moenkhausia sanctaefilomenae (Steindachner, 1907) was studied at 15 lakes of the Cuiaba river floodplain, Mato Grosso. The sex ratio, the timing of reproduction, spawning type and the length of first gonadal maturation were analyzed. We sampled 212 individuals (108 females and 104 males) from June of 2005 to March of 2006. There was not significant difference in the sex ratio, considering the whole period sampled. The biggest frequency of matured females was found in December in all of the lakes. The mean width of the ovarian follicles varied among the periods in December it was larger than others. What it suggests that the spawning happened, probably, among the end of December or beginning of January. That corresponds to the high water and flood in the area. The frequency distribution of the width of the ovarian follicles showed a polimodal pattern. That suggest parceled out spawning, but restricted to the period of December to March. The mean length of gonadal maturation was estimated in 33.9 mm. There was a positive relationship between length of first maturation and the asymptotic length. In synthesis, the data indicate that the reproduction happens in a synchronous way in all of the lakes sampled.

Dinâmica populacional de quatro espécies de grandes bagres na bacia do rio Cuiabá, Pantanal norte, Brasil (Siluriformes, Pimelodidae)

The length structure of the stocks of four species of large Pimelodidae catfishes was used to study the dynamics of their populations in the Cuiaba river basin, north Pantanal. The estimative of the growth parameters, recruitment and mortality rates for the species were obtained. Among the species studied the Barbado presented the fastest growth than the others. The Pintado, Cachara and Jau exhibited similar growth rate. For the Barbado and the Pintado we observed two annual picks of recruitment, however the Cachara and the Jau presented a single annual pick. The analysis of the mortality indicates that the fishing is a source of mortality more important for the Barbado than for the other species.

Variação temporal e espacial na composição de guildas alimentares da ictiofauna em lagoas marginais do Rio Cuiabá, Pantanal Norte

O presente trabalho teve como objetivo avaliar a variacao espacial e temporal das guildas alimentares das comunidades de peixes em 10 lagoas marginais do Rio Cuiaba no Pantanal. As lagoas foram amostradas em tres periodos do ciclo hidrologico (inicio e final da seca e inicio da enchente de 2005). As guildas alimentares foram determinadas atraves da analise do conteudo estomacal das especies mais abundantes da comunidade. Foram analisadas 37 especies pertencentes a oito guildas alimentares (insetivora, herbivora, onivora, zooplanctivora, planctivora, detritivora, bentivora e iliofaga), as quais variaram espacial e temporalmente. Observamos uma mudanca na composicao das guildas troficas entre os periodos e locais analisados, porem o numero de guildas nao variou espaco-temporalmente. Nossos resultados sugerem que as mudancas espaciais e temporais na composicao das guildas podem estar relacionadas com diversos fatores, como as alteracoes na composicao da comunidade onde novas especies podem compor as diferentes guildas; a exploracao de recursos mais abundantes em determinadas epocas do ano favorecendo a presenca de algumas guildas somente em alguns periodos.

Spatial and temporal distribution of fish larvae in marginal lagoons of Pantanal, Mato Grosso State, Brazil

An analysis was made of the spatial and temporal distribution of the abundance and composition of fish larvae assemblies, aiming to ascertain correlations with biotic and abiotic factors in marginal lagoons of the Cuiaba River floodplain in Brazils Pantanal wetlands. Samples were collected bimonthly in the pelagic region of the marginal lagoons (fourteen lagoons) close to the littoral zone covered by aquatic macrophytes from December 2006 to April 2007. The captured individuals consisted of 2,739 larvae, represented predominantly by Triportheus spp. (Characidae), Parodontidae, Anostomidae, Characidae and Serrasalmidae. Larval density varied among the sample lagoons in December, but the biotic (zooplankton density) and abiotic (water temperature, electrical conductivity, dissolved oxygen, pH, water transparency and lagoon depth) factors did not significantly affect larval composition and abundance. Larvae were captured throughout the sample period, with the highest densities occurring in December and early January. Temporally, lagoon depth, water transparency and fluviometric level showed a negative correlation with larval density. Both the zooplankton and the larval density vary positively, responding likewise to the environmental conditions imposed by flooding. The highest larval density was also found to coincide with the first rains (early December), when the rainfall has not yet reached its peak.

A dimensão espacial e temporal da diversidade de peixes da zona litoral vegetada de lagoas marginais da planície de inundação do rio Cuiabá, Pantanal, Brasil

The present work has evaluated the spatial and temporal distribution of fish species richness of the vegetated littoral zone of 15 marginal lagoons in the floodplain of the Cuiaba River, Pantanal. The lagoons were sampled in three periods along of the dry season (June, September and December of 2005), through nine sieve throws distributed systematically at a minimum distance of five meters from each other. We caught 12,784 individuals belonging to seven orders, 21 families and 98 species of fish. Most of the captured species were rare and presented restricted geographical distribution. Drought intensification did not affect the spatial species distribution and the loss of species as dry season proceeded was proportional in the different orders. The total abundance of individuals as well as the richness varied with time. Rarefaction curves indicated that the reduction in richness was an artifact of the reduction in the abundance of individuals. When we compared the estimated richness under a same abundance level we did not find difference among the richness of species in the beginning and at the end of the dry season. Richness estimators indicated that to distribute the samples in the time was an appropriate strategy to reduce the problem of the false absences and to improve the efficiency of the sampling. Thus, our results suggest that for the design of reserves in the Pantanal, areas with a large number of lagoons of different forms and sizes would conserve the regional fish diversity, as the distribution of most small size species is restricted to a few lagoons.

Reproductive biology of pacu Piaractus mesopotamicus (Holmberg, 1887) (Teleostei: Characidae) in the Cuiabá River Basin, Mato Grosso, Brazil

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 Cuiaba River basin, the first of these encompassing its headwaters (Cuiabazinho River - Rosario Oeste) and the other the flood area of the Cuiaba River (Porto Cercado - Pocone). 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.

Gametogenesis and reproductive cycle of Melanorivulus aff. punctatus (Boulenger, 1895) (Cyprinodontiformes, Rivulidae) in Chapada dos Guimarães, Mato Grosso, Brazil

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 Melanorivulusaff. punctatus were collected in a permanent dam in Chapada dos Guimaraes, 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 spermatozoa was free in the lumen and the duct. This can indicate a continuous reproductive cycle with split spermiation. The females had gonads in the development stage from May to September with undifferentiated and differentiated oogonias and early oocytes always facing the lumen, abundant pre-vitellogenic and vitellogenic oocytes and some atresias. In the phase capable of spawning, observed from October to March, the mature oocytes are abundant, there are many post-ovulatory complexes and some atresia in advanced stage. The regression, observed in some individuals from February to April, is characterized by ovaries with many atresias and post-ovulatory complexes. The same results were found in the quantitative assessments. Therefore, it may be characterized as discontinuous cycle with split spawning. Thus, the reproductive cycle of this species can be characterized as continuous for males and discontinuous for females, which have a most intense phase of reproduction from October to March. However, both have fractional release of gametes.

Effect of abiotic variables on fish eggs and larvae distribution in headwaters of Cuiabá River, Mato Grosso State, Brazil

O estudo do ictioplâncton tem se mostrado uma importante ferramenta na identificacao de areas e periodos de desova para as especies de peixes de agua doce.Amostragens de ictioplâncton foram realizadas mensalmente na regiao de cabeceira do rio Cuiaba, bacia do alto rio Paraguai, (Mato Grosso, Brasil) e em quatro de seus tributarios, entre novembro de 2007 e marco de 2008, com o objetivo de avaliar a distribuicao espaco-temporal de ovos e larvas de peixes. Foram amostrados 22.067 ovos e 1.045 larvas. Identificou-se correlacao significativa e negativa entre a densidade de ovos, o nivel fluviometrico e a vazao. A densidade de larvas nao apresentou correlacao significativa com nenhuma das variaveis regionais. As densidades, tanto de ovos quanto de larvas, foram significativamente maiores nos pontos no rio principal. As maiores abundâncias foram observadas em ambientes com maiores valores de largura do rio, valores intermediarios de profundidade e menores valores de O2 dissolvido, condutividade e transparencia. Os grupos taxonomicos de larvas mais abundantes foram Anostomidae, Zungaro zungaro, Bryconamericus spp., Pimelodus spp., Pimelodidae, Auchenipteridae e Siluriformes, com maiores abundâncias observadas nos pontos no rio principal. Os resultados mostram que o local de estudo e uma importante area de desova para as especies de peixes migradores e nao-migradores, e destacamos a importância do rio principal para o evento reprodutivo, pela influencia das variaveis locais, transparencia e largura do rio, que por sua vez parecem ser influenciadas temporalmente pelo nivel fluviometrico.

Persistence and stability of cichlid assemblages in neotropical floodplain lagoons

In this study, we evaluated how cichlid assemblages are affected by seasonal and interannual variations in water volume in the floodplain lagoons of the Cuiabá River in the Pantanal wetland. Eleven lagoons were sampled in the early dry season and the early rainy season over a three-year period. Analysis of similarity (ANOSIM) showed that the species compositions and relative abundances were distinct between the seasons, which indicates that neither persistence nor stability was maintained on a seasonal basis. However, the interannual comparisons show the opposite tendency, indicating strong stability and persistence on an annual basis. These results indicate that the cichlid assemblages in these lagoons have two equilibrium points, one in the early dry season and the other in the early rainy season, and that the assemblages alternate between these points through the hydrologic cycle. In addition to the effect of the water level variation, the abundance distribution is also affected by conductivity and pH, which also influence the total abundance of the species in the assemblage.