Plasticity in the diet of Astyanax taeniatus in a coastal stream from south-east Brazil

Abstract

In this work we aimed to characterise the diet of Astyanax taeniatus (Jenyns 1842) (Characiformes, Characidae) along the Mato Grosso stream and we hypothesised that the diet of this species would vary according to spatial, seasonal and ontogenetic differences. Specimens were collected every second month at three sites with different physical attributes. The feeding habits of 651 specimens were analysed using the Alimentary Index (IA i ). Analysis of the diet showed an effect of spatial, temporal and ontogenetic factors. Vegetal allochthonous items were more important in the diet of Astyanax taeniatus in upstream sites while animal autochthonous items were more important downstream. Ontogenetic differences in the diet were significant only in upstream sites, where adults consumed a greater amount of vegetal matter than juveniles. These results reinforce the idea that Astyanax species are opportunistic and show trophic plasticity.Keywords: feeding, opportunism, stream fish. Plasticidade trófica em Astyanax taeniatus de um riacho costeiro do Sudeste do Brasil ResumoNeste trabalho, objetivou-se caracterizar a dieta de Astyanax taeniatus (Jenyns 1842) (Characiformes, Characidae) ao longo do Rio Mato Grosso, com a hipótese de que a espécie apresente variações espaciais, sazonais e ontogenéticas. Os exemplares foram coletados bimestralmente em três localidades, que diferiram pelas variáveis físicas. As preferências alimentares foram analisadas a partir de 651 exemplares, utilizando-se o Índice Alimentar (IA i ). Foram avaliadas diferenças espaciais, sazonais e ontogenéticas a partir dos dados de dieta. Os itens de origem vegetal e alóctone foram mais importantes na dieta da espécie para as localidades com maior altitude, enquanto os itens animais e autóctones, na localidade baixa. Na dieta de jovens e adultos, houve diferença significativa na contribuição de itens de origem vegetal e animal somente na localidade mais alta, onde os adultos consumiram maior quantidade de matéria vegetal. Os resultados reforçam a ideia de que as espécies de Astyanax possuem hábito alimentar onívoro e oportunista, evidenciando sua alta plasticidade alimentar ao longo do riacho.Palavras-chave: alimentação, oportunismo, peixe de riacho.

Importance of allochthonous resources in the diet ofAstyanax aff. fasciatus (Osteichthyes: Characidae) in streams: a longitudinal approach

“…fasciatus consumed a wide range of food items and there was a predominance of allochthonous resources in the diet, particularly insects and plants, along the longitudinal gradient. Several studies in streams, involving the diet of fish fauna, reveal the importance of allochthonous subsidies to many species (Esteves & Aranha 1999, Lowe-McConnell 1999, Casatti 2002, Silva et al 2012, especially for the genus Astyanax , Borba et al 2008, Wolff et al 2009, Ferreira et al 2011, Ferreira et al 2012, Manna et al 2012. Specifically for A. aff.…”

“…The headwaters region is influenced by the surrounding vegetation, which contributes with allochthonous material (plant material and terrestrial insects), as the stream enlarges, decreases the importance of importing terrestrial organic matter. The riparian vegetation is well documented in the literature as a major supplier of food for aquatic organisms (Vannote et al 1980, Polis et al 1997, Baxter et al 2005, Manna et al 2012, Silva et al 2012, in turn controlling the flow of nutrients. The shading produced by riparian vegetation limits the autotrophic production, and fish depend on resources from the slopes for feeding (Lowe-McConnell 1999).…”

“…Subsidies as invertebrates can represent up to half of the energy in the diet of stream fish (Masson & Macdonald 1982), indicating that in these environments the availability of prey induce higher consumption (Rezende & Mazzoni, 2006), or the fishes have a preference for these organisms (Main & Lyon 1988, Garman 1991. The importance of subsidies in the diet of stream fish has been frequently reported in tropical regions (Henry et al 1994, Vitule et al 2008, Wolff et al 2009, Tó foli et al 2010, Manna et al 2012, Small et al 2013.…”

“…In rivers and streams there is a remarkable longitudinal gradient of food resources dominant in the fish diet, and in headwaters regions fish depend primarily on allochthonous material, made up of terrestrial insects and plant debris (Lowe-McConnell 1975). Manna et al (2012) observed that the diet of Astyanax taeniatus varied according to physical characteristics of the environment, showing a reduced amount of allochthonous resources (mostly plant debris) along the longitudinal gradient of the stream.…”

“…Species of the genus Astyanax are considered flexible in the use of food resources in streams, and have been described as opportunistic with high feeding plasticity (Wolff et al 2009, Manna et al 2012. However several studies have shown the predominance of allochthonous resources, especially insects and higher plants (leaves, fruits and seeds) in the diet of these fish in streams , Borba et al 2008, Ferreira et al 2011), even those with little vegetation cover (Borba et al 2008).…”