This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/ dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems.

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The biodiversity of many Brazilian rivers is seriously threatened by industrial and municipal pollution, and Rio Paraiba do Sul, located between two major industrial centers is one example of this situation. A survey of the fish assemblage was conducted from October 1998 to September 1999 and the data were used to develop an index of biotic integrity (IBI). We sampled three zones in bracketing a large urban-industrial complex to evaluate water quality changes and the usefulness of the IBI as a monitoring tool. Water quality was classified as poor upstream of the effluent discharges, very poor near the discharges, and poor-fair downstream of the discharges, with this latter situation revealing the current biological capacity of the river. Physical and chemical habitat characteristics were also measured at each site to construct an independent environmental index to validate the IBI. The habitat and IBI indices were highly correlated, suggesting this IBI would be applicable to other large rivers in southeast Brazil.

ABSTRACT. Diversity of fish assemblages in the four geographic units of the Paraíba do Sul river. Diversity patterns of fish assemblages along the four geographic units (upper, middle-upper, middle-lower and lower reaches) of the Paraíba do Sul river were studied aiming to assess spatial (geographic units) and seasonal (wet/dry periods) variations. Twenty-five sites were sampled between December 2002 and March 2003 (summer/wet) and, August to November 2003 (winter/dry). Fish were caught by a standardized effort, using gill nets, cast nets and mesh trays. A total of 81 species were recorded comprised in 9 orders, 29 families and 55 genera. Characiformes showed the highest number of species (28) followed by Siluriformes (23). Perciformes, mainly Tilapia rendalli and Geophagus brasiliensis, and Cyprinodontiformes, mainly Poecilia vivipara and Poecilia reticulata, were the most numerically abundant groups, while Siluriformes, mainly Hypostomus luetkeni, and Perciformes, mainly Geophagus brasiliensis showed the highest biomass. Poecilia vivipara was recorded only in dry period. Spatially, Hoplosternum littorale predominated in the middle-upper reaches, Pimelodus fur, Hypostomus luetkeni, Glanidium albescens in the middle-lower, and Loricariichtys spixii and Prochilodus lineatus, in the lower reach. Number of species and Margalef's richness showed an increase from the upper to the lower river reaches, mainly during the wet period. Species widely distributed along all over the river extent (G. brasiliensis, Oligosarcus hepsetus e P. reticulata) are opportunistic and can use the available resources despite poor environmental conditions, reflecting the state alteration of the river. Differentiation on the physiography throughout the longitudinal extent of the basin does not match shifts in fish assemblages, suggesting that factors associated to habitat alterations could be structuring fish community at local scale. KEYWORDS.Fish assemblages, spatial patterns, fish distribution, ichthyofauna, neotropical rivers. espécies e a riqueza de Margalef apresentaram um aumento do trecho superior para o inferior, principalmente durante o período de cheia. Espécies que apresentaram ampla distribuição ao longo do rio (G. brasiliensis, Oligosarcus hepsetus e P. reticulata) são consideradas oportunistas por se aproveitarem dos recursos disponíveis em ambientes pobres, refletindo o estado de alterações do rio. Diferenciações na fisiografia ao longo da extensão longitudinal da bacia não coincidiram com mudanças nas assembléias de peixes, sugerindo que fatores associados a alterações de hábitats poderiam estar estruturando a comunidade de peixes a nível local. PALAVRAS-CHAVE.Assembléias de peixes, padrões espaciais, distribuição de peixes, ictiofauna, rios neotropicais.O rio Paraíba do Sul é um dos mais utilizados sistemas lóticos do Brasil, por situar-se entre os maiores centros urbano-industriais do país, e tem sofrido alterações de origem antrópica ao longo dos últimos quatro séculos. A intensa urbanização e industrialização são os mai...

A index of biotic integrity (IBI)

Cyprinodontiformes fishes (guppies) are widely distributed in Neotropical regions and use deteriorated microhabitats in rivers where few species can occur. This study was carried out in a stretch of the Paraíba do Sul River in bracketing a large urban-industrial complex. The aim was to assess eventual effects that the industrial complex could have on distribution of two closely related fish species of guppies, Phalloceros caudimaculatus and Poecilia reticulata. The area was divided into three zones: Z1, 40 km upriver of the major urban-industrial complex of Volta Redonda; Z2, just down river of the complex; and Z3, 30 km down river of the complex. Six sites (two in each zone) were sampled monthly between November 1998 and October 1999, using a standardized fishing effort with cast net throws, trays lifts and seine hauls, covering different microhabitats, that is, riffles, pools and the proximity of the river's margins. Poecilia reticulata was widely distributed, peaking at Z2, the most polluted area, while P. caudimaculatus showed the highest abundance at Z3, being almost absent in Z1. Both species occurred in high numbers throughout the year but they were scarce between April and June. Females outnumbered males for both species in most size classes and at all sites. Juveniles were more abundant than adults, with non-pregnant females outnumbering pregnant ones. Condition factor was always higher in males than females but only males P. reticulata showed significant difference among the three zones, with the highest values at Z2. The higher number of females confirms the expectation that these species can use very polluted areas and that availability of food provided by organic loads allowed their distribution all over the area. Although these two species have shown indication of spatial separation in the study area, their similar seasonal patterns of occurrence suggest that they respond in a similar way to changes in environmental conditions. Keywords: pollution, distribution, Cyprinodontiformes, population structure, Paraíba do Sul River. Redonda; Z2, imediatamente abaixo do complexo industrial; e Z3, 30 km abaixo do complexo. Seis locais (dois em cada zona) foram amostrados mensalmente entre novembro de 1998 e outubro de 1999, usando um esforço de pesca estandardizado com tarrafas, peneiras e arrastos, cobrindo diferentes microhábitats, isto é, corredeiras, remansos e a proximidade da margem dos rios. Poecilia reticulata foi largamente distribuído, apresentando pico na Z2, área mais poluída, enquanto P. caudimaculatus apresentou a maior abundância na Z3, sendo quase ausente na Z1. Ambas as espécies ocorreram em elevados números ao longo do ano, mas foram escassas entre abril e junho. Fêmeas foram mais numerosas do que machos para ambas as espécies na maioria das classes de tamanho e em todos os locais. Jovens foram mais abundantes que adultos, com fêmeas não grávidas predominando sobre fêmeas grávidas. Fator de condição foi sempre maior nos machos do que nas fêmeas, mas somente machos de P. reticulata a...

This work aims to analyze changes in the fish assemblages along a longitudinal reaches of the rio Paraíba do Sul, one of the most used Brazilian aquatic systems, to assess the river "health" and to identify eventual recovery trends. Standardized monthly samplings were carried out at six sites, from October 1997 to September 1999, using casting, sieves, seine and gill nets. Three zones were searched: upstream (Z I), downstream (Z III) and nearby the source of pollution (Z II). Three univariate distribution methods were used: ABC (abundance-biomass curves), K-dominance curves, and geometric class's distribution. Additionally, cluster analysis was applied to detect eventual patterns. The ABC and K-dominance curves showed Z II with evident indication of stress in both yearly cycles, followed by Z III and Z I. Few rare species and absence of common species in Z I, presence of common and abundant species, mainly opportunist, in Z II, and the highest number of rare species in Z III, was the overall pattern showed by geometric class. Number of fish was higher at Z II, while number of species did no change significantly among zones. Cluster analysis separate Z II samples from Z I and III. All the three univariate methods showed evident signals of stress at Z II, which showed indication of organic enrichment as expressed in the high abundance of common species, although physicochemical variables (ammonia, nitrogen, total phosphorous and DBO) have increased slightly from Z1 to Z III. A lesser stress condition was shown at the downstream zone (Z III), indicating the river recovery capacity. The use of biological indicators in this study proved to be a better tool to assess non-point sources pollution when compared to traditional physicochemical measurements.Objetiva-se no presente trabalho, analisar mudanças nas assembléias de peixes ao longo de um trecho longitudinal do rio Paraíba do Sul, um dos sistemas aquáticos mais usados do Brasil, para avaliar a "saúde" do rio e identificar eventuais tendências de recuperação. Amostragens mensais foram realizadas em seis locais, de outubro de 1997 a setembro de 1999, utilizando redes de espera, tarrafas, peneiras e picaré. Foram atribuídas três zonas para avaliar as assembléias de peixes: Z II (complexo industrial da cidade de Volta Redonda -fonte da poluição), Z I (montante do complexo industrial) e Z III (jusante do complexo industrial). Três métodos univariados foram usados: ABC (curvas de abundância-biomassa), curvas de K-dominância, e distribuição por classes geométricas. Adicionalmente, foram aplicadas análises de agrupamento para verificar padrões de distribuição das espécies. A curva ABC e a curva de K-dominância indicaram maior estresse para a Z II, em ambos os ciclos anuais seguido pelas Z III e I. A classe geométrica apresentou um padrão de poucas espécies raras e ausência de espécies comuns para a Z I, presença de espécies comuns e abundância de espécies oportunistas para a Z II, e maior número de espécies raras na Z III. O número de indivíduos foi maior na Zona II, enqu...

1. We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil. 2. Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40-1080 m and distances of 0.1-188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site. 3. A total of 2684 individuals in 16 families and 59 species were recorded. 4. Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within-class and mean betweenclass similarities in assemblage data. 5. Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure. 6. Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence. 7. These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts.