We investigated the trophic niches and the resource partitioning of two snook species, the common (Centropomus undecimalis) and the fat snook (C. parallelus), in four tropical estuaries of the northeastern Brazil, using stable isotope analyses of carbon (δ13C) and nitrogen (δ15N). Fish specimens, mainly juveniles, basal resources and a primary consumer were collected in 2015 during dry and rainy seasons in all estuaries, which exhibited differences in system size, geomorphologic shapes, levels of sea access and anthropic pressures. Potential effect of factors like fish body length, estuary and seasonality on isotope ratios were investigated. Positive relationships between the size of fish and δ15N values were found, regardless the species. Our results indicated that snooks can be characterized as secondary consumers and have close trophic niches in most estuaries. Trophic overlaps were more pronounced within the largest estuaries (Catuama and Santa Cruz), whereas smaller systems that have restricted connections to the sea presented low isotopic niche overlap between both species (Suape and Sirinhaém). Moreover, a higher variability of δ13C and δ15N values in snooks was found in larger estuaries undergoing stronger influences from coastal adjacent waters. Although we were not able to detect clear seasonal effects, greater isotopic overlaps were found during the rainy season. Despite the lack of intrinsic differences in life history traits, both species, dominated by juveniles, shared similar trophic niches in these environments. Highlights ► δ 13 C and δ 15 N of two Centropomidae were investigated in four estuaries in Brazil. ► Juveniles of Centropomus undecimalis and C. parallelus have close isotopic niches. ► Trophic overlaps were more pronounced in large estuaries. ► Resource partitioning process might reflects the resource availability in estuaries.

Ecological guilds have been widely applied for understanding the structure and functioning of aquatic ecosystems. This study describes the composition and the spatio-temporal changes in the structure of the fish fauna and the movements between the estuary and the coast of a tropical estuary, the Itapissuma/Itamaracá Complex (IIC) in northeastern Brazil. Fish specimens were collected during the dry and rainy seasons in 2013 and 2014. A total of 141 species of 34 families were recorded. Almost half of the species (66 species, 47%) were exclusive to the estuary and 50 species (35%) to the coast; 25 (18%) were common to both environments. Marine species were dominant in both richness and biomass as they explore the environment during part of their life cycle, whereas estuarine species were dominant in abundance. Marine stragglers displayed a higher richness, abundance and biomass in the coastal waters. The estuarine environment was dominated by zoobenthivores in terms of richness, while detritivores prevailed in abundance and biomass. Zoobenthivores had the highest richness and abundance in coastal waters, while piscivores had the highest biomass. The IIC supports a rich fauna with a diverse trophic structure and is an important feeding and development area for migratory species.

The present study describes the spatial and temporal structure of the estuarine fish community in the internal sector of the Amazon Estuary. Samples were obtained in the main channels and tidal creeks of Guajará and Marajó Bays and Guamá River. A total of 41,516 fish specimens were collected, representing 136 taxa, 38 families and 12 orders. In the dry season, the mean salinity of the main channel increased along a limnicmarine gradient, between the Guamá River and the Marajó Bay. Species richness was lowest in the mouth of the Guamá River and in the right margin of the Guajará Bay. Fish species composition and environmental guilds differed markedly among areas: Migrants and Freshwater Stragglers were dominant in the Guamá River and the Guajará Bay, while Estuarine, Marine Stragglers and Migrants predominated in the Marajó Bay. However, the trophic guilds were still relatively well balanced, in functional terms. Piscivores and Zoobenthivores were the dominant feeding functional groups in all the studied areas. In this study, the assessment of the community and the use of the guild approach were efficient to describe the structure and functioning of the assemblages of estuarine fish also helping to assess the anthropogenic pressures in the area.

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Abstract. The presently reported study provides length-weight relations (LWR) of 70 fi sh species (Actinopterygii) from the tropical coastal region of Pernambuco, Northeast Brazil: