Trophic ecology of Acestrorhynchus falcirostris Cuvier, 1819 in island lakes on the lower stretch of the Solimões River, Amazon Basin

Abstract 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.

Resumo O objetivo deste estudo foi determinar a ecologia trófica de juvenis e adultos de Acestrorhynchus falcirostris durante o período de enchente e cheia em seis lagos de ilha adjacentes ao rio Solimões. Assim, investigamos: i) a posição trófica, através do nicho trófico fracional; ii) a largura de nicho; iii) sobreposição de nicho; iv) a estratégia alimentar. Os espécimes foram coletados durante os anos de 2014 a 2017, utilizando redes de emalhar com malha variando de 30 a 120mm entre nós opostos. Por meio da análise do conteúdo estomacal, observamos a preferência no consumo de itens de origem animal. Os juvenis consumiram insetos em maiores proporções (IAi% = 50%), enquanto os adultos consumiram preferencialmente peixes (IAi% = 99,98%). Apesar da grande oferta de alimentos disponíveis no período da cheia, os juvenis eram os únicos a consumir itens de origem alóctone, como por exemplo, os insetos. Os juvenis apresentaram uma estratégia alimentar e composição alimentar diferente para os adultos. Os juvenis foram considerados onívoros com uma estratégia generalista, enquanto os adultos foram considerados piscívoros com uma estratégia alimentar mais especialista. Assim, a composição alimentar, amplitude do nicho, posição trófica e a estratégia alimentar de Acestrorhynchus falcirostris muda em função do estágio de desenvolvimento.

Trophic ecology of Acestrorhynchus falcirostris Cuvier, 1819 in island lakes on the lower stretch of the Solimões River, Amazon Basin / Ecologia trófica de Acestrorhynchus falcirostris Cuvier, 1819 em lagos de ilha no trecho inferior do Rio Solimões, Bacia Amazônica

Abstract 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.

Resumo O objetivo deste estudo foi determinar a ecologia trófica de juvenis e adultos de Acestrorhynchus falcirostris durante o período de enchente e cheia em seis lagos de ilha adjacentes ao rio Solimões. Assim, investigamos: i) a posição trófica, através do nicho trófico fracional; ii) a largura de nicho; iii) sobreposição de nicho; iv) a estratégia alimentar. Os espécimes foram coletados durante os anos de 2014 a 2017, utilizando redes de emalhar com malha variando de 30 a 120mm entre nós opostos. Por meio da análise do conteúdo estomacal, observamos a preferência no consumo de itens de origem animal. Os juvenis consumiram insetos em maiores proporções (IAi% = 50%), enquanto os adultos consumiram preferencialmente peixes (IAi% = 99,98%). Apesar da grande oferta de alimentos disponíveis no período da cheia, os juvenis eram os únicos a consumir itens de origem alóctone, como por exemplo, os insetos. Os juvenis apresentaram uma estratégia alimentar e composição alimentar diferente para os adultos. Os juvenis foram considerados onívoros com uma estratégia generalista, enquanto os adultos foram considerados piscívoros com uma estratégia alimentar mais especialista. Assim, a composição alimentar, amplitude do nicho, posição trófica e a estratégia alimentar de Acestrorhynchus falcirostris muda em função do estágio de desenvolvimento.

Influence of abiotic factors on the composition of fish assemblages in the Aracá-Demeni sub-basin of the middle Negro River.

We evaluated the influence of flooding and receding comparison and spatial variation on the composition and structure of fish assemblages in blackwater and clearwater rivers of the Aracá-Demeni sub-basin in the middle Negro River, Amazonas state, Brazil. The collections were carried out during the falling-water period (November 2018) and the rising-water period (April 2019) using gillnets with meshes ranging from 30 to 120mm stretched mesh size. Ecological estimates of richness, equitability, the Shannon-Wiener diversity index, and the Berger-Parker index showed no significant differences between the periods. The composition of the ichthyofauna showed variations between the falling-water and rising-water periods. Beta diversity in the Aracá-Demeni sub-basin is almost completely caused by species substitution, with spatial turnover accounting for most of the estimate. The identification of these patterns and of the responsible factors are fundamental for the definition of conservation strategies, especially in an ecosystem whose dynamics can be influenced by climate change through changes in the intensity of the flood pulse and connectivity.

The consumption of fish by the riverine population of the lower Solimões River, Amazonas, Brazil.

The riverine population of the Amazon Basin are among the largest consumers of fish in the world, but the consumption patterns could be regionally distinct. Moreover, their total fish catches are not fully known. The objective of this work was to estimate the per capita fish consumption of the riverine people that inhabit the Paciência Island (Iranduba, Amazonas), where there is a fishing agreement in force. A total of 273 questionnaires were applied during the first two weeks of each month between April 2021 and March 2022. The sample unit was the residences. The questionnaire contained questions about the species captured and their quantities. Consumption was calculated by dividing the average monthly capture with the average number of residents per household interviewed, which was multiplied by the number of questionnaires applied. Thirty groups of consumed fish species belonging to 17 families and 5 orders were recorded. The total catch was 3,388.35 kg and the highest monthly catch was 602.60 kg during the falling-water season in October. Daily per capita fish consumption averaged 66.13 ± 29.21 g/day, with a peak of 116.45 g/day during the falling-water season in August. The high fish consumption rate highlighted the importance of fisheries management to food security and the maintenance of the community's lifestyle.

Trophic ecology of Acestrorhynchus falcirostris Cuvier, 1819 in island lakes on the lower stretch of the Solimões River, Amazon Basin.

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.

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought / Variações do fator de condição de quatro espécies de Characidae de lagos de várzea da Amazônia como função do tempo e da posição trófica: efeitos de uma seca anômala

Abstract The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two omnivores, Colossoma macropomum and Mylossoma duriventre, exhibited trends consistent with their life cycles in 2004 and 2006: high values during the hydrologic seasons of high water, receding water, and low water, with a drop following reproduction following the onset of rising water. However during the drought year of 2005 the condition factor was much lower than normal during receding and low water seasons, probably as a result of an abnormal reduction in resource availability in a reduced habitat. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. We suggest that if predictions of increasing drought in the Amazon are correct, predatory species may benefit, at least in the short run, while omnivores may be negatively affected.

Resumo Os efeitos de secas extremas sobre peixes de água doce ainda é globalmente desconhecido. Neste artigo, nós estimamos o fator de condição, uma medida relativa de bem estar baseada na relação entre e peso do corpo e o comprimento, em quatro espécies de peixes de lagos da Amazônia, pertencentes a dois níveis tróficos (onívoros e carnívoros), capturadas durante três anos consecutivos: 2004, 2005 (quando ocorreu uma seca anômala) e 2006. As duas espécies onívoras, Colossoma macropomum e Mylossoma duriventre exibiram tendências consistentes com seu ciclo de vida nos anos de 2004 e 2006: valores mais altos na cheia, vazante e seca, seguida por uma queda na enchente que coincide com a estação reprodutiva. No entanto, o fator de condição foi muito menor durante a seca e a enchente em 2005, provavelmente devido a redução anormal na disponibilidade de recursos em um habitat reduzido. As duas espécies piscívoras, as piranhas Serrasalmus spilopleura e S. elongatus, mantiveram relativa estabilidade nas estimativas do fator d condição, ao longo do ciclo hidrológico dos três anos, sem efeito aparente da seca extrema, provavelmente porque a redução do habitat foi contrabalanceada pelo aumento na densidade de presas. Caso as predições de aumento de frequência de secas extremas venha a se confirmar, acreditamos que espécies predadoras poderão ser beneficiadas, ao menos no curto prazo, enquanto as onívoras serão negativamente afetadas.

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought.

The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two omnivores, Colossoma macropomum and Mylossoma duriventre, exhibited trends consistent with their life cycles in 2004 and 2006: high values during the hydrologic seasons of high water, receding water, and low water, with a drop following reproduction following the onset of rising water. However during the drought year of 2005 the condition factor was much lower than normal during receding and low water seasons, probably as a result of an abnormal reduction in resource availability in a reduced habitat. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. We suggest that if predictions of increasing drought in the Amazon are correct, predatory species may benefit, at least in the short run, while omnivores may be negatively affected.

Ecomorphological correlates of twenty dominant fish species of Amazonian floodplain lakes / Correlações ecomorfológicas de vinte espécies de peixes dominantes em lagos de várzea da Amazônia

Abstract Fishes inhabiting Amazonian floodplain lakes exhibits a great variety of body shape, which was a key advantage to colonize the several habitats that compose these areas adjacent to the large Amazon rivers. In this paper, we did an ecomorphological analysis of twenty abundant species, sampled in May and August 2011, into two floodplain lakes of the lower stretch of the Solimões River. The analysis detected differences among species, which could be probably associated with swimming ability and habitat use preferences.

Resumo Os peixes que habitam os lagos de várzea da Amazônia apresentam morfologias bastante diversas, possibilitando a exploração bem sucedida dos diferentes habitats que formam estas áreas adjacentes aos grandes rios amazônicos. Neste artigo, relatamos os resultados de uma análise ecomorfológica de vinte espécies abundantes, coletadas em maio e agosto de 2011, em dois lagos das várzeas do trecho inferior do rio Solimões. As analises indicaram diferenças entre as espécies como função do atributos ecomorfológicos, provavelmente associadas com a capacidade natatória e com preferências por habitat.

Ecomorphological correlates of twenty dominant fish species of Amazonian floodplain lakes.

Fishes inhabiting Amazonian floodplain lakes exhibits a great variety of body shape, which was a key advantage to colonize the several habitats that compose these areas adjacent to the large Amazon rivers. In this paper, we did an ecomorphological analysis of twenty abundant species, sampled in May and August 2011, into two floodplain lakes of the lower stretch of the Solimões River. The analysis detected differences among species, which could be probably associated with swimming ability and habitat use preferences.

Fish diversity of floodplain lakes on the lower stretch of the Solimões river.

The fish community of the Solimões floodplain lakes was studied by bimonthly samples taken from May 2001 to April 2002. These were carried out at lakes Maracá (03 degrees 51'33"S, 62 degrees 35'08,6"W), Samaúma (03 degrees 50'42,1"S, 61 degrees 39'49,3"W), and Sumaúma and Sacambú (03 degrees 17'11,6"S and 60 degrees 04'31,4"W), located between the town of Coari and the confluence of the Solimões and Negro rivers. Collections were done with 15 gillnets of standardized dimensions with several mesh sizes. We collected 1,313 animals distributed in 77 species, belonging to 55 genera of 20 families and 5 orders. Characiformes was the most abundant Order, with a larger number of representatives in the Serrasalmidae and Curimatidae. The most abundant species in the samplings were Psectrogaster rutiloides (132 individuals), Pigocentrus nattereri (115 individuals), and Serrasalmus elongatus (109 individuals). Lakes Samaúma, Sacambú, and Sumaúma were adjusted to logarithmic and lognormal series. The diversity exhibited an inverse gradient to the river flow, showing the highest diversity at Lake Sumaúma, followed by Samaúma, Sacambú, and Maracá. Species richness estimated through the jackknife technique ranged from 78 to 107 species.

Fish diversity of floodplain lakes on the lower stretch of the Solimões River

O estudo das comunidades de peixes dos lagos de várzea do Rio Solimões foi realizado no trecho compreendido entre o município de Coari e a confluência com o Rio Negro, nos Lagos Maracá (03º51'33"S e 62º35'08,6"W), Samaúma (03º50'42,1"S e 61º39'49,3"W), Sumaúma e Sacambú (03º17'11,6"S e 60º04'31,4"W), no período de maio de 2001 a abril de 2002, por meio de coletas bimensais realizadas com 15 redes de espera de dimensões padronizadas, com diversos tamanhos de malhas. Foram capturados 1.313 indivíduos distribuídos em 77 espécies, pertencentes a 55 gêneros de 20 famílias e 5 ordens. Characiformes foi a ordem mais abundante, com maior número de representantes nas famílias Serrasalmidae e Curimatidae. As espécies mais freqüentes foram: branquinha Psectrogaster rutiloides, com 132 indivíduos, piranhas Pigocentrus nattereri, com 115 indivíduos, e Serrasalmus elongatus, com 109 indivíduos. Os Lagos Samaúma, Sacambú e Sumaúma ajustaram-se aos modelos Série Logarítmica e Lognormal. O Lago Sumaúma apresentou maior diversidade, seguido de Samaúma, Sacambú e Maracá. A riqueza de espécies estimada oscila entre 78 e 107 espécies.