The presence of aquatic macrophytes is a key factor in the selection of habitats by fish in floodplain lakes because these plants enhance the physical and biological complexities of aquatic habitats. The seasonal flood pulse may influence this interaction, but there is no information in the literature about the effects that flood events may have on macrophytes assemblages and its associated effects on fish assemblages. Thus, this article aimed to investigate whether species richness, evenness and similarities in fish assemblage composition differed between littoral areas vegetated with macrophytes and unvegetated areas, before and after a flood. We sampled three lakes in the floodplain of the upper Paraná River basin. Sampling was conducted before (December 2004 and January 2005) and after (early March, late March and May 2005) a flood event. Overall, species richness and evenness were higher in macrophytes-covered areas. Before the flood, the composition of fish assemblages was distinct when comparing vegetated and unvegetated areas. After the flood, the similarity in fish assemblage composition was higher, indicating a homogenization effect of floods for fish inhabiting littoral areas of floodplain lakes. After the flood, opportunistic species dominated the fish assemblages in aquatic macrophytes, apparently restructuring assemblages in the littoral, restarting a succession process. Thus, the observed homogenization effect of the flood could minimize biological interactions and could induce fish assemblages to begin a new process of structurization.
We describe the fish assemblages associated with drifting macrophyte mats and consider their possible role as dispersal vectors in the Ivinhema River, a major tributary of the upper Paraná River, Brazil. Fish associated with drifting mats were sampled in the main river channel during January and March 2005, when the wind and/or the increased water level were sufficient to transport macrophyte stands. Fish in the drifting mats were sampled with a floating sieve (4 m long x 2 m wide x 0.6 m high, and 2 mm mesh size). In the laboratory, larvae, juvenile, and adult fish were counted and identified to the lowest possible taxonomic level. In four drifting macrophyte mats we captured 218 individuals belonging to at least 28 species, 17 families, and 6 orders. Aphyocharax dentatus, Serrasalmus spp., and Trachelyopterus galeatus were the most abundant taxa associated with the mats, but species richness ranged from 6 to 24 species per mat. In addition, 85% of the total number of individuals caught was larvae and juveniles. Although preliminary and based on limited samples, this study of drifting macrophyte mats was the first one in the last unregulated stretch of the Paraná River remaining inside Brazilian territory, and alerts us to the potential role of macrophytes mats as dispersers of fish species in the region.Nesse trabalho as assembleias de peixes associadas a bancos de macrófitas flutuantes à deriva foram descritas. Além disso, foi considerado o possível papel desses bancos como vetores de dispersão no rio Ivinhema, importante tributário do alto rio Paraná, Brasil. Os peixes associados aos bancos à deriva foram amostrados no canal principal desse rio, entre os meses de Janeiro a Março de 2005, quando o vento e/ou o aumento no nível da água foram suficientes para transportar os bancos de macrófitas. Os peixes foram amostrados com uma rede flutuante (4 m de comprimento x 2 m de largura x 0,6 m de altura e 2 mm de tamanho de malha). No laboratório, larvas, jovens e adultos foram contados e identificados ao menor nível taxonômico possível. Nos quatro bancos de macrófitas flutuantes a deriva foram capturados 218 indivíduos pertencentes à pelo menos 28 espécies, 17 famílias e 6 ordens. Aphyocharax dentatus, Serrasalmus spp. e Trachelyopterus galeatus foram os táxons mais abundantes associados aos bancos de macrófitas à deriva, mas a riqueza de espécie variou entre 6 e 24 espécies por banco. Além disso, 85% do total do número de indivíduos capturados foram larvas e juvenis. Embora preliminar e baseado em amostragens limitadas, este estudo, conduzido em bancos de macrófitas flutuantes à deriva, foi o primeiro no último trecho não regulado do rio Paraná em território brasileiro, e alerta para o papel potencial que os bancos de macrófitas têm como dispersores de peixes na região.
RESUMO.O objetivo deste estudo foi identificar os principais processos (locais e/ou regionais) que influenciam a composição e a estrutura das assembléias de peixes em reservatórios do Estado do Paraná. Foram amostrados seis reservatórios (Capivari, Guaricana, Alagados, Fiú, Mourão e Rio dos Patos). As coletas foram trimestrais (de julho/95 a fevereiro/97 e de março/98 a fevereiro/99), com uso de redes de espera simples e tresmalhos, de diferentes malhagens, expostas por 24 horas. Todos os exemplares foram identificados, medidos, pesados e a abundância das espécies foi expressa pela captura por unidade de esforço (CPUE), dada em número (n o ind./ 1000m 2 de rede* 24h). Variáveis abióticas (processos locais) também foram medidas no momento de coleta. A análise de correspondência com remoção do efeito do arco (DCA) e a análise de componentes principais (PCA) foram utilizadas para sumarizar os dados de abundância e abióticos, respectivamente. Os escores dos eixos dessas análises foram utilizados para avaliar a relação entre os fatores abióticos (locais e regionais) e a estrutura das assembléias de peixes. Os processos regionais parecem ser os principais responsáveis pela composição e, conseqüentemente, pela estrutura das assembléias de peixes nos reservatórios.Palavras-chave: processos locais e regionais, assembléias de peixes, reservatórios, Estado do Paraná, Brasil.ABSTRACT. Influence of local and regional processes on fish Assemblager in reservoirs of Paraná State, Brazil. The aim of this study was to identify the main processes (local and/or regional) that influence in the composition and structure of fish assemblages in reservoirs located in the state of Paraná. Six reservoirs were sampled (Capivari, Guaricana, Alagados, Fiú, Mourão and Rio dos Patos). The samples were quarterly taken from July/95 to February/97 and March/98 to February/99 using gillnets and trammel nets of different mesh sizes set for 24 hours. The abundance was indexed by the catch per effort in number (No. ind./ 1000m 2 net* 24 hs). All fishes collected were identified, measured and weighted. Some abiotic variables (local process) were measured during the samples. The detrended correspondence analysis (DCA) and the principal components analysis (PCA) were applied to summarize abundance data and abiotic variables, respectively. The scores of the axis retained for interpretation in both analyses were used to assess the relation between abiotic variables (local and regional) and fish assemblage structure. The regional processes appeared to exert strong influence on the composition and, consequently, on the structure in the reservoirs of fish assemblage.
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