Longitudinal changes on ecological diversity of Neotropical fish along a 1700 km river gradient show declines induced by dams

Material suplementario en: 10.1016/j.pecon.2024.03.003.In naturally flowing waters, communities are expected to increase their taxonomic and functional diversity as well as increase the complexity of food web architecture along the longitudinal gradient from headwaters to mouth. However, these theories do not necessarily apply to dammed rivers. We analysed fish communities at 12 locations along the 1700 km stretch of the transnational Uruguay River. We determined species richness, beta-diversity and its components (turnover and nestedness), trophic diversity, and isotopic niches at community level, with particular focus on areas upstream and downstream of the four existing dams. We estimated trophic diversity metrics based on diet analysis, and isotopic niche breadth based on Bayesian isotopic niche models. We detected consistent longitudinal changes, supporting predictions from the River Continuum Concept. However, taxonomic richness, trophic diversity, and isotopic niche decreased abruptly immediately downstream of dams, and the component contributing the most to beta diversity was turnover, with the highest values occurring mainly after the cascade of dams in the upper Uruguay River, fitting expectations from the Serial Discontinuity Concept. The dam-free stretches of the Uruguay River allowed the recovery of ecological diversity as fish richness and trophic and isotopic niche increased. The negative impacts of dams should urgently be considered in the Neotropics, where many large dams are projected.ANII: FCE_2_2016_1_126780CSIC: I+D 2016 577-34

Diets and trophic structure of fish assemblages in a large and unexplored subtropical river: The Uruguay river

This article belongs to the Special Issue Trophic Interactions in Warm Freshwater EcosystemsThe Neotropics represent a hotspot for freshwater biodiversity with vast number of fish species of scarce ecological knowledge. This holds true for the Uruguay River, where fish assemblages and their diets remain unexplored. Fish assemblages were surveyed in 14 sites along the river main course, from headwaters to mouth (approximately 1800 km), with the aim to identify the trophic roles of fishes and to describe trophic structure of these assemblages, following standardized sampling campaigns and laboratory procedures. One hundred species (2309 gut contents) were analysed and classified into four trophic groups subdivided into eight lower-level groups: Piscivore, piscivore-invertivore, detritivore, omnivore-detritivore, omnivore-invertivore, omnivore-planktivore and omnivore-herbivore. The trophic structure of the assemblages varied along the river, with the relative species richness of fish consuming terrestrial invertebrates increasing towards the middle river section, probably driven by the large floodplains in that areas, supporting global theories such as the flood pulse concept. This study describes the feeding habits of fish along the Uruguay River, being the first dietary description for 29 species. This knowledge is essential for management and conservation, serving as baseline in the context of future environmental changes while generating novel evidence on the functioning of ecosystems in this scarcely studied climatic region

Ectoparasites of Nile tilapia (Oreochromis niloticus) in cage farming in a hydroelectric reservoir in Brazil

For this study, we performed a parasitological analysis of cage-cultured Nile tilapia (Oreochromis niloticus) from the Agua Vermelha Reservoir, Southeastern Brazil, and verified relationships with limnological data, seasonality, and fish growth phase. From March 2010 to March 2011, sixty-three specimens of O. niloticus in three growth phases (i.e., initial, intermediate, and final) were collected. All fish specimens were infested with at least one ectoparasite species (prevalence = 100%). Five species of protozoans (Trichodina compacta, Trichodina magna, Ichthyophthirius multifiliis, Piscinoodinium pillulare, and Epistylis sp.) and five species of monogenoids (Cichlidogyrus halli, Cichlidogyrus thurstonae, Cichlidogyrus sp. 1, Scutogyrus longicornis, and Gyrodactylus sp.) were observed. The abundance of Trichodina spp. and the prevalence of Epistylis sp. were higher in the dry season, and the prevalence of C. halli was higher in the rainy season. For the majority of ectoparasites found in this study, fish in the intermediate and final phases had higher parasitism rates than those in the initial phase. The data presented may help fish farmers to understand the parasite dynamics of the fish species studied in cage-farming systems.O presente estudo teve como objetivo realizar análise parasitológica de tilápias-do-Nilo, (Oreochromis niloticus) criadas em tanques-rede no Reservatório de Água Vermelha, Sudeste do Brasil, bem como verificar suas inter-relações com as características limnológicas, sazonalidade e fase de criação. Durante o período de março de 2010 a março de 2011, espécimes de O. niloticus, pertencentes a três fases de criação (inicial, intermediária e final), foram colhidos, totalizando 63 indivíduos. Todos os peixes estavam infestados por pelo menos uma espécie de ectoparasita (prevalência = 100%). Foi observada a ocorrência de cinco espécies de protozoários (Trichodina compacta, Trichodina magna, Ichthyophthirius multifiliis,Piscinoodinium pillulare e Epistylissp.), assim como cinco espécies de monogenóides (Cichlidogyrus halli, Cichlidogyrus thurstonae, Cichlidogyrus sp. 1,Scutogyrus longicornis e Gyrodactylussp.). A abundância de Trichodina spp. e prevalência de Epistylis sp. foram maiores no período seco, e a prevalência de C. halli foi maior no período chuvoso. Para a maioria dos ectoparasitas encontrados neste estudo, os peixes pertencentes às fases intermediária e final apresentaram maiores taxas de parasitismo do que aqueles pertencentes à fase inicial. Os dados apresentados neste estudo podem ser de grande importância para piscicultores, de forma a auxiliá-los no conhecimento da dinâmica dos parasitas da espécie de peixe estudada em sistemas de tanques-rede.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Agência Paulista de Tecnologia dos Agronegócios – APTA, Secretaria de Agricultura e Abastecimento, Polo Regional do Noroeste Paulista, Votuporanga, SP, BrasilDepartamento de Parasitologia, Instituto de Biociências, Universidade Estadual Paulista – UNESP, Botucatu, SP, BrasilFAPESP: 2010/01424-0CNPq: 577649/2008-