Food spectrum and trophic structure of the ichthyofauna of Corumbá reservoir, Paraná river Basin, Brazil

Abstract

In this paper we evaluate plasticity of fish concerning diet. We expect that sampling over a large temporal and spatial scale, including environmental changes such as impoundments, will allow us to cover most of the diet plasticity. We also evaluate the efficacy of ordination method in discriminating trophic groups based on fish species diet. Data were obtained from 17 sampling stations sampled monthly from March/96 to February/99 in the Corumbá river drainage, before and after the formation of the Corumba reservoir. Diet was determined analysing 9,177 stomach contents from 64 fish species. Trophic categories were discriminated by a non-hierarchic grouping analysis named k-means, applied to diet data. Most of the species presented great trophic plasticity, eating a great variety of food items. Resources availability, estimated from all fish stomach contents, was similar among environments, except in creeks, where it varied more with a large importance of terrestrial insects. K-means present satisfactory results, identifying nine trophic groups (detritivores, herbivore-piscivores, insectivore-herbivores, omnivores, invertivores, aquatic insectivores, piscivore-insectivores, piscivores and herbivores).Neste estudo avaliamos a plasticidade trófica em peixes. Nós esperamos que amostras obtidas com uma ampla escala temporal e espacial, incluindo mudanças ambientais como represamentos, nos permita cobrir a maior parte desta plasticidade. Foi avaliada também a eficiência do método de ordenação em discriminar os grupos tróficos baseado na dieta das espécies. As amostragens foram realizadas mensalmente de março/96 a fevereiro/99 em 17 estações de coleta na bacia do rio Corumbá antes e após a formação do reservatório de Corumbá. Foram analisados 9177 conteúdos estomacais, pertencentes a 64 espécies. As categorias tróficas foram discriminadas através de uma análise de agrupamento não hierárquica denominada K-means aplicada aos dados de dieta. A maioria das espécies apresentou elevada plasticidade trófica, consumindo uma grande variedade de itens alimentares. A disponibilidade dos recursos alimentares, estimada através de todos os conteúdos estomacais, foi similar entre os ambientes a exceção dos riachos, onde ocorreu maior heterogeneidade e os insetos terrestres tiveram grande importância. A análise K-means revelou resultados satisfatórios, identificando nove grupos tróficos (detritívoros, herbívoro-piscívoros, insetívoro-herbívoros, onívoros, invertívoros, insetívoros aquáticos, piscívoro-insetívoros, piscívoros e herbívoros).

Effects of river damming in Neotropical piscivorous and omnivorous fish: feeding, body condition and abundances

“…In response to the increase in prey availability an increase in the piscivorous abundance was observed. Similar patterns have been reported for other reservoirs (Agostinho et al, 1999;Luz-Agostinho et al, 2006;Bennemann et al, 2011). This was also observed in the present study as the sites that presented the higher increases in prey abundance (DO and RE) also presented the higher increases in piscivorous abundance, as observed for H. aff.…”

“…This was also observed in the present study as the sites that presented the higher increases in prey abundance (DO and RE) also presented the higher increases in piscivorous abundance, as observed for H. aff. malabaricus and O. longirostris, specialist piscivorous (Hahn & Fugi, 2008), that do not change their diet despite environmental changes, and for A. lacustris and P. britskii (opportunist piscivorous), in which the fish consumption was sporadic or even inexistent (Cassemiro et al, 2005;Luz-Agostinho et al, 2006). This increase in specialist piscivorous abundance can be due to the increase in prey availability, that is highlighted by the great participation of forage species as Astyanax dissimilis, Crenicichla spp.…”

“…The feeding plasticity in Neotropical fish has been shown for a great number of species (Hahn et al, 1998;Abelha et al, 2001;Luz-Agostinho et al, 2006). Thus, fish respond to the low availability of preferential resources by changing its behaviour to consume different items as the preferential ones become scarce (Dill, 1983).…”

“…Dominant species in a new reservoir are small-sized, with feeding plasticity, low longevity and high reproductive performance (opportunist strategy, sensu Winemiller, 1989), denoting advantages in the colonisation process (Agostinho et al, 1999). This small sized species become an abundant resource and explains the success of piscivores after impoundments (Luz- Agostinho et al, 2006;Bennemann et al, 2011).…”

“…The high availability of allochthonous resource in the environment, may cause a positive effect in the production of all trophic levels, an event known as the trophic upsurge period (Kimmel & Groeger, 1986;O'Brien, 1990;Gubiani et al, 2011). The high availability of small body size species in the new environment should increase the frequency of fish with a carnivorous fish diet (Novakowski et al, 2007) or even lead some omnivorous species to piscivory (Luz- Agostinho et al, 2006;Delariva et al, 2007). Although the nutritional quality of a fish-based diet should be higher than one based on other items, such as invertebrates, due to its high protein (Anthony et al, 2000) and energy content (Davis et al, 1998), the organism's response to this consumption should differ according to the species diet in the natural environment.…”