ABSTRACT. Fish diet studies contribute to understanding resource partitioning and community trophic structure. The present paper characterizes the diet of "peixe-cachorro" species Acestrorhynchus britskii and A. lacustris in Sobradinho reservoir, Bahia State, Brazil. Bimonthly samples (November 2006 to July 2008 were taken in the lotic, transition and lentic stretches of the reservoir, using gillnets overnight. A total of 899 A. britskii and 476 A. lacustris stomachs were analyzed, 70% of which were empty. Their content indicated the species are predominantly piscivorous, with 18 prey fish species identified. However, each prey occurred in a single month, except for Anchoviella vaillanti, recorded in 80% of months for A. bristski, and Tetragonopterus chalceus in 25% for A. lacustris. The species presented high food overlap (Cλ = 0.992), owing to the occurrence of Actinopterygii (bits) and Actinopterygii in all months. Regarding prey fish alone, a differentiated intake and lower food overlap was detected, in the flood (Cλ = 0.427) and drought (Cλ = 0.172) seasons, in the lotic (Cλ = 0.434), transition (Cλ = 0.089) and lentic (Cλ = 0) stretches, and in overall overlap (Cλ = 0.236). The spatial and seasonal differences in the intake of different prey fish by both species suggest an opportunistic feeding habit and a competition reduction mechanism for food resources.Keywords: natural feeding, peixe-cachorro, piscivory. RESUMO. Composição da dieta e sobreposição alimentar deAcestrorhynchus britskii e A. lacustris (Characiformes: Acestrorhynchidae) do reservatório de Sobradinho, rio São Francisco, Estado da Bahia. Estudos sobre a dieta de peixes contribuem para o entendimento da partilha de recursos e da estrutura trófica da comunidade. O presente trabalho caracteriza a dieta dos peixes-cachorro Acestrorhynchus britskii e A. lacustris no reservatório de Sobradinho, Estado da Bahia. Coletas bimestrais noturnas (Novembro/2006 a Julho/2008) foram efetuadas nos trechos lótico, transição e lêntico do reservatório, empregando redes de espera. Foram analisados 899 estômagos de A. britskii e 476 de A. lacustris, aproximadamente 70% dos quais se encontravam vazios. Seu conteúdo evidenciou tratar-se de espécies predominantemente piscívoras, com 18 peixes-presa identificados. Entretanto, cada presa ocorreu num único mês, exceto Anchoviella vaillanti, registrada em 80% dos meses para A. bristski e Tetragonopterus chalceus em 25% deles para A. lacustris. As espécies apresentaram elevada sobreposição alimentar (Cλ = 0,992), pela ocorrência de Actinopterygii (partes) e Actinopterygii não-identificado em todos os meses. Entretanto, considerando apenas os peixespresa, foi observado consumo diferenciado e menor sobreposição alimentar, nos períodos de cheia (Cλ = 0,427) e seca (Cλ = 0,172), nos trechos lótico (Cλ = 0,434), de transição (Cλ = 0,089) e lêntico (Cλ = 0), e na sobreposição geral (Cλ = 0,236). A diferença espacial e sazonal no consumo de peixes-presa distintos pelas duas espécies sugere hábito alimentar oportunista e mecanis...
Cymothoid fish parasites settle on hosts in ways that may impact fish health and energetics. High abundances of Artystone minima observed in Nannostomus beckfordi from the Jeju River in eastern Amazonia were investigated to answer the following questions: (a) What factors are associated with the high prevalence at this locality?; (b) Is high abundance associated with co‐infestation of alternative hosts?; and (c) Is parasite presence associated with host species growth and/or reproduction? Fish assemblages were sampled quarterly (August 2017–May 2018) from five habitats along with environmental data. Parasitic indices were calculated, and parasite presence used to evaluate differences in growth of hosts using analysis of covariance considering host sex and sampling season (wet vs. dry). Parasites were only abundant in one of the habitats, a large, shallow backwater bay with macrophytes. Abiotic environmental factors (flow and depth) likely impact parasite transmission and are, therefore, particularly important in producing these local patterns. Two secondary hosts, Hyphessobrycon cf. rosaceus and Moenkhausia collettii, were found in the wet season. Based on host biology compared to other fish in the habitat, parasite infestation is inferred to be depth associated and long‐term infestation is apparently limited in alternative hosts. Parasite presence was significantly associated with reduced weight (standardized for length) of female Nannostomus beckfordi in the wet season. Furthermore, ovaries of non‐parasitized females from the wet season presented a range of maturation stages, while parasitized females were all immature, indicating a significant association of parasites with host reproductive capacity. Abstract in Portuguese is available with online material
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