Community structure of the demersal fish of Sepetiba Bay, RJA year-long otter trawl survey in the Sepetiba Bay, Rio de Janeiro State, Brazil, was carried out in order to describe the fish community structure and their spatial and seasonal variations. Sampling carried out between July 1993 and June 1994, yielded 97 species, 70 genera and 38 families. Ariidae, Gerreidae, Sciaenidae, Carangidae and Sparidae families amounted 69,9% of the total catch in number, and Ariidae, Sparidae, Gerreidae, Haemulidae and Sciaenidae amounted 67,9% of the total weight. Genidens genidens, Gerres aprion, Cathorops spixii, Micropogonias furnieri and Chloroscombrus chrysurus were the most numerous species, each one contributing more than 5% of the total catches. Higher numbers of fishes were associated with low depths and transparencies of the inner Bay, while salinity is a quite stable environmental parameter ranging around 29%o most of the time all over the Bay. Numbers of fish are higher in Late Summer and Early Winter. Overall, most number and weight of fishes were higher in the inner Bay than in the outer area next to the sea limit, while the number of species was higher in the outer Bay. The high number of fish species suggests the important role played by the Sepetiba Bay as rearing and residence grounds for the fish community.Key words: Sepetiba Bay, ichthyofauna, coastal lagoons, fish, community. RESUMOUm programa de amostragens mensais de arrasto de fundo em sete estações de coleta na Baía de Sepetiba foi realizado entre julho de 1993 e junho de 1994 com o objetivo de descrever a estrutura da comunidade de peixes e suas variações espaciais e temporais. Noventa e sete espécies de peixes foram levantadas, compreendendo 70 gêneros e 38 famílias. As famílias Ariidae, Gerreidae, Sciaenidae, Carangidae e Sparidae, nesta ordem, foram as mais abundantes em número, contribuindo com 69,9% do total capturado, enquanto Ariidae, Sparidae, Gerreidae, Haemulidae e Sciaenidae somaram 67,9% do peso total. Genidens genidens, Gerres aprion, Cathorops spixii, Micropogonias furnieri e Chloroscombrus chrysurus, nesta ordem, foram as espécies mais abundantes, contribuindo cada uma com mais de 5% do número total de peixes capturados. O maior número de peixes foi associado às menores profundidades e transparências, enquanto a salinidade apresentou, na maior parte do tempo, valores estáveis em torno de 29%o. Maiores abundâncias de peixes ocorreram entre fins do verão e início do inverno. O número e peso dos peixes foram maiores na zona interna da Baía enquanto

While there is already a comprehensive understanding of the effects of environmental variables, such as dissolved oxygen, temperature and salinity, on the structure, biomass and metabolism of aquatic biota in estuarine habitats, the effect of sedimentation, a harmful underlying factor, remains unclear. The aim of this study was to assess the differences in fish assemblages along the freshwater to salt water gradient of a large tropical estuary, and to evaluate the effects on them of habitat disturbance associated with shallow water sedimentation in the intertidal areas. Fish and environmental variables were recorded in the upper, middle and lower salinity zones of the estuary at ebb tide in both the dry and wet seasons. Sediment samples associated with different levels of habitat disturbance were analysed using granulometry, and their organic content and dissolved oxygen levels were quantified. Water temperature, salinity, pH and dissolved oxygen levels were also measured. Habitat disturbance was found to be correlated with the density, biomass and richness of fish assemblages. A total of 77 species were recorded, forming two distinct fish assemblages, with the Eleotridae family dominating in the upper zone, and Gerreidae, Gobiidae and Tetraodontidae the most common in the middle and lower estuary. Changes in the structure of fish assemblages, including reductions in density, biomass and richness, were associated with disturbance to natural features, where muddy sediment was replaced by sandy sediment and the quantity of organic matter fell. Atherinella brasiliensis was the species which showed a preference for the disturbed areas in the middle and lower zones, while Dormitator maculatus showed a preference for them in the upper estuary. They may be taken as indicators of habitat disturbance due to shallow sedimentation.

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ABSTRACT. DISTRlBUTlON AND RELATl VE ABUNDANCE 01' THE MARINE CATFISH (SILU-RI FORMES, ARIIDAE) lN SEPETIBA BAY, RIO DE JANEIRO. Marine catfish (Ariidae) are abundant resources in olter trawl fisheries carried oul aI Sepeliba Bay, Rio de Janeiro (La!. 22°54, 23°04'S; Long. 43°34', 44°10' W). Rel alive abllndance and distribution were assessed, based in 158 fi shing sampling at seven sites in lhe Bay, between July-1993 e June-1996. Five species were recorded in the following abundance rank order: Genidens genidens (Valenciennes, 1839), Calhorops f>pixii (Agassiz, 1829), Sciadeichlhys lunisculis (Valenciennes, 1840), Neluma barba (Lacépede,1803), and Bagre marinus (Milchill , 1814), the lalter have been caught in only two samples. Marine catfish showed higher abundance in lhe inner Bay, wilh indication of spatial segregation. G. genidens was abundant in ali sites ofthe inner Bay, C. spixii e N. barba, nearto rivers mouths, and S. lunisculis, being widespread in ali studied area. Sazonality was nol evident, with few exceptions in some of the three annllal cycles; G. genidens and S. /unisculis were more abundant in biomass in summer 1994/95 (G. genidens) and 1993/94 (s. lunisculú). G. genidens e N. barba show higher abundance (CPUE and biol1lass) between July-93 and June-95 and C. f>pixii e S hmisculis between July-95 and June-96. Total associalion index indicates a overall positive assoc iation al110ng ali species, with. higher Jaccard and Sorensen silllilarities coeftici ent for the pairs C. spixii/G. genidens, G. genidens/S. lunisculis, e C. spixii/S ltmisculis. Pearson linear correlation and Sperlllan rank indicate that G. genidens and N. barba are inversely correlated to C. spixii and S /unisculis. Spatial segregation strategy Illay be explaining the coexistence 01' the Illarine catfish at Sepetiba Bay. K.EY WORDS. Siluriformes, Ariidae, fish rcology, marine catfish, Sepetiba Bay A família Ariidae compreende os bagres marinhos e de água salobra, ocorrendo na zonas tropicais litorâneas, em águas pouco profundas e geralmente de fundo lodoso. Em geral procuram a desembocadura dos rios, estuários e regiões lagunares na época da desova (FIGUEIREDO & MENEZES 1978). São largamente

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The rio Santo Antônio is a perennial lowland stream in the Brazilian semi-arid region, and is the main tributary of the upper rio Paraguaçu, an important drainage of the Chapada Diamantina. The temporal variation of the fish composition and abundance in a stretch of the middle course of the river was evaluated. Sampling was carried out monthly between August 1998 and July 1999, using standardized gear and techniques. Data on water and air temperature, water transparency, maximum and mean depth, width and area of the channel, and flow were recorded on each fish sampling occasion. Univariate and multivariate statistical analyses were employed in order to detect significant temporal differences in environmental parameters and fish abundance. Temperature, transparency and channel depth drove opposite tendencies between the dry and rainy months. The fish community richness (32) and composition did not change between these periods, but large fish caught with gillnets were more abundant in the rainy months. We conclude that the undramatic disturbance in the hydrological stream conditions between the dry and rainy periods led to weak responses of the fish assemblage. Long-term monitoring would be necessary, however, to assess the real persistence of the fish community structure in this perennial stream.