The aim of this study was to analyse the trophic ecology of speckled peacock bass Cichla temensis inhabiting two tributaries of the middle Negro River, the Aracá River and the Demeni River. Using an analysis of stomach contents and stable isotope composition (δ15N, δ13C) of scales, we describe the diet and evaluate the trophic position of subadult and adult individuals. We then test whether diet shifts and trophic positions occurred among successive size classes and among sample locations. The stomach content analysis confirmed the piscivorous feeding habit of the species and showed that the speckled peacock bass preyed on a variety species belonging to different trophic guilds. The length of the ingested prey increased with the size of the speckled peacock bass. Diet composition and trophic position were not different among size classes. δ13C values yielded significant shifts among the size classes: larger individuals displayed higher δ13C values than smaller individuals. Trophic position varied between locations, with lowest values observed in fish from the Aracá River. This study demonstrated that diet of C. temensis may vary according to the size of the fish, even at the subadult or adult stages, and according to the river/locality, even within a same basin. We then suggest that further studies take into account local availability of food resources to better explore C. temensis diet and tropic ecology.

Summary This study aimed to estimate the parameters of length‐weight relationship for 16 freshwater fish species that inhabit the Aracá and Demeni Rivers, which are two tributaries of the Negro River (Amazonas state, Brazil). The fishes were sampled using gillnets (15 × 2 m, mesh size 30–120 mm between opposite knots), during 6 days each year, in April 2016, November 2018 and April 2019. The gillnets were placed in the river twice each day; in the morning (5–9 a.m.) and in the evening (5–9 p.m.), with a standardized time of 4 hr. Measurements were taken for standard length (SL – 0.1 cm precision) and total weight (TW – 0.01 g precision). The parameters a and b of the equation WT = a.LTb were estimated. This study also provides new data on of maximum lengths for six species, namely, Argonectes longiceps, Hemiodus atranalis, Chalceus erythrurus, Astrodoras asterifrons, Trachydoras steindachneri and Acarichthys heckelii.

Parameters of the length‐weight relationship (LWR) were calculated for five fish species from Amazon Basin. Samplings were carried out in ten lakes of the Solimões River floodplains during the four seasons of the hydrological cycle: rising water, high water, receding water, and low water, during two periods. The first period of eight years included samplings performed from 2001 to 2008 and the second sampling period of two years was from 2012 to 2013. Specimens were captured using gillnets (mesh sizes ranging from 30 to 120 mm between opposite knots) and standardized dimension of 20 m in length × 2 m in height. This study provides the LWR parameters for Acarichthys heckelii, Leporinus trifasciatus, Brycon amazonicus, Curimatella meyeri and Osteoglossum bicirrhosum.

This research reports the LWR of ornamental fish from floodplain lakes of the Solimões River basin. The fish were caught in the Paciência island (a fluvial island) in two lakes Sacambú and Cacau using purse seine 7 m × 4 m and mesh size = 3 mm, once during the flood in June 2017 and dry in January 2018. The specimens captured were anesthetized using eugenol 15 mg · L–1, fixed formalin 10% and stored ethanol 70% after 10 days. This study provides the LWR parameters for the species Anablepsoides micropus, Anchoviella jamesi, Cichlasoma amazonarum, Heros efasciatus, Ctenobrycon hauxwellianus, Copella nattereri and Hemigrammus levis. The parameter a ranged from 0.0092 to 0.0229, b ranged from 2.78 to 3.50 and the R2 ranged from 0.985 to 0.998. The results represent new information about ornamental fish from floodplain lakes, with new LWR for five species that are not present in FishBase data set and probably are new for science. This study is preliminary and much work needs to be done especially in the Solimões River floodplain areas and with our research we hope to encourage new studies in the region.

As mudanças climáticas, principalmente em decorrência das ações antrópicas, têm sido causas de impactos ambientais a nível regional e global. Dentre as regiões do planeta, a região Amazônica é uma das mais prejudicadas pelos impactos das mudanças climáticas que têm se manifestado por meio de eventos extremos com sérias implicações para a biodiversidade mais rica e endêmica do planeta. Diante disso, o objetivo deste trabalho foi discutir os efeitos das mudanças climáticas sobre os peixes amazônicos. Tais efeitos induzem ao aumento da temperatura, oscilações nos níveis de oxigênio e alterações no ciclo hidrológico em decorrência dos eventos de secas e inundações extremas. Nos peixes, esses efeitos têm implicações biológicas comprometendo a fisiologia das espécies; ecológicas com significativas alterações nos aspectos reprodutivos, alimentares e migratórios, além de variações na abundância e riqueza das espécies; as quais eventualmente terão consequências diretas na produção pesqueira. Os efeitos das mudanças climáticas na ictiofauna necessitam ser investigados e avaliados profundamente para que estratégias de conservação e manejo possam ser traçadas a fim de assegurar a manutenção da biodiversidade íctica na amazônia.

Length‐weight relationship parameters were calculated for six fish species from São Marcos Bay, in Northeast Brazil (the segment between 02°35′55″S and 44°20′58″W; 02°34′53″S and 44°21′48″W; 02º42′25″S and 44º26′46″W). The specimens were caught quarterly from April 2010 to February 2013, using monofilament gillnets (2, 4 and 6 cm between knots) from 100 m to 3,000 m long and 4 m to 6 m high. The present study covers a much wider size range for four species and adds new information for the maximum length of Notarius bonillai.

Although many upstream effects of a dam on the trophic ecology of fish have been reported, little is known about their downstream effects on the isotopic niche of Amazonian predator fish. The authors used stable isotope analysis of δ 13 C and δ 15 N to determine the downstream effects of damming of the Uatumã River on the niche width, carbon energy sources and trophic position of peacock bass Cichla temensis comparing with a free-flowing river in the Amazon basin, Brazil, during the peak flood and early falling water period of 2020. They found that the C. temensis population of the undammed river had a smaller niche width than the C. temensis population of the dammed river, despite the greater number of prey trophic levels utilized and the higher trophic position of C. temensis individuals. The results demonstrate that in both rivers there is a gradual shift in the contribution of prey fish sources to the diet of C. temensis throughout its growth, even among adult individuals. They conclude that the isotopic niche of C. temensis was altered by damming during the period of late high water to early low water in the Uatumã River.

The aim objective of this study was to determine the trophic ecology of juvenile and adult Acestrorhynchus falcirostris during the rising and flood (high-water) period in six island lakes adjacent to the Solimões River. As such, we investigated: i) the trophic position, through the fractional trophic niche; ii) the niche breadth; iii) niche overlap and iv) the food strategy of the species. The specimens were collected during the years 2014 to 2017, using gillnets with mesh sizes ranging from 30 to 120mm between opposite knots. Through the analysis of stomach contents, the preference in the consumption of items of animal origin was observed. Juveniles consumed insects in greater proportions (IAi% = 50%), while adults consumed fish (IAi%=99,98%). Despite the large supply of food items available in the high-water period, juveniles were the only ones to consume items of allochthonous origin, such as insects. Juveniles presented a different dietary strategy and dietary composition to adults. Juveniles were omnivores with a generalist strategy, while adults were piscivores with a specialist strategy. Thus, the food composition, niche breadth, trophic position and feeding strategy of Acestrorhynchus falcirostris change due to the stage of development.