Abstract This study aims to evaluate the dynamics of fish trophic guilds according to the longitudinal gradient of the Paraguay River, northern Pantanal, Brazil. Three river segments were sampled: plateau, confluence and plain. These segments have different physical and biological characteristics, with high water flow in forest areas in plateau and slow flow in meanders, with Pantanal typical vegetation. In total, 26,542 individuals distributed in 130 fish species were collected. The sampled species were characterized in seven trophic guilds. From the seven trophic guilds identified, only three were statistically related to the type of the environment; herbivores were more abundant in the plateau, piscivores in the confluence, and invertivores in the plain. According to values of corrected Akaike Information Criteria, the environmental variable that best explains the abundance of piscivorous fishes in the segments sampled in the Paraguay River was water transparency. For herbivores, the model that explained the variation in abundance was composed by temperature, altitude and dense forest proportion. The variable altitude best represented the abundance of invertivores. Water transparency, temperature, altitude, river width and dense forest proportion were determining factors for the distribution of piscivorous, herbivorous and invertivorous fishes as a response to an environmental gradient that meets its ecological requirements. Understanding the trophic relationships is fundamental for management actions, contributing to the maintenance of ecosystem services of different species. Therefore, future research must be taken into account regarding management and ecological relationships.

Resumo O objetivo desse estudo foi analisar a ocorrência de danos nucleares nas hemácias de Gymnotus inaequilabiatus, expostos in vivo ao herbicida glifosato. Os peixes foram distribuídos em quatro grupos, sendo eles: controle (sem a adição do herbicida) e os grupos contaminados nas concentrações de 65 µg/L (concentração permitida pela Resolução do CONAMA), 1 mg/L (limite máximo recomendado pela Organização Mundial de Saúde - OMS e Food and Agriculture Organization - FAO) e de 5 mg/L (superdose, cinco vezes maior que a estabelecida pela OMS e FAO). Para análise de danos celulares foi utilizado o método de Anormalidades Nucleares Eritrocíticas (ANE) contando 1000 células por lâmina em duplicatas. Foi observado um aumento nos danos celulares durante as 144 horas de exposição (6 dias) em todos os tratamentos. Mesmo sob uma pequena concentração, houve um claro efeito sobre a formação segmentada, renal, lobada e principalmente na formação de micronúcleos. Os elevados danos foram causados nas primeiras 48 horas sendo reduzidos após 144 horas, onde o peixe pode ter bloqueado o efeito do herbicida. Estudos que analisam os mecanismos de ação de herbicidas à base de glifosato, são fundamentais para a determinação dos riscos causados à biota, já que há grande divergência sobre os limites máximos toleráveis na água, podendo causar impactos na qualidade e integridade desses ecossistemas.

Abstract This study analyzed the occurrence of nuclear damage in the red blood cells of Gymnotus inaequilabiatus (Valenciennes, 1839), exposed in vivo to the herbicide glyphosate. The fish were distributed in four groups, namely: control (without addition of herbicide) and contaminated groups with application of 65 µg/L (concentration allowed by CONAMA Resolution), 1 mg/L (maximum limit recommended by the World Health Organization - WHO and Food and Agriculture Organization - FAO) and 5 mg/L (overdose, five times higher than that by WHO and FAO). For the analysis of cell damage, the method of Nuclear Erythrocytic Abnormalities (NEA) was used, containing 1000 cells for duplicate elimination. An increase in cell damage was observed for 144 hours (6-days) of exposure in all controls. Even under a small concentration, there was a clear effect on segmented, renal, lobed formation and mainly on the formation of micronuclei. The high damage was caused in the first 48 hours and reduced after 144 hours, where the fish can have the herbicidal effect blocked. Studies that analyze the mechanisms of action of glyphosate-based herbicides are essential to determine the risks caused by biota, since there is a great divergence on the maximum tolerable limits in water, which affect quality and integrity of these ecosystems.