Influence of flood pulses on diet composition and trophic relationships among piscivorous fish in the upper Paraná River floodplain

Abstract

The aim of this article is to evaluate whether alterations in flood pulses differentially affect diet composition, feeding niche breadth, and diet overlap of piscivorous fish. Species examined were Acestrorhynchus lacustris, Hoplias aff malabaricus, Plagioscion squamosissimus, Rhaphiodon vulpinus, and Salminus brasiliensis. These species were collected with gillnets (different mesh sizes) in the upper Paraná River floodplain, during four distinct flood events (four periods; A = 1992/ 1993; B = 2000; C = 2001; and D = 2002). The volumetric method was chosen to express diet results. Feeding niche breadth was calculated using Levins measure, and diet overlap was evaluated by the Pianka's Index. Flooding was more intense and lasted longer in the first period (1992/1993-A). Diet composition of the studied species was broad (47 total items consumed). For period A, Prochilodus lineatus was the main item taken by four out of five species. In the other periods, there were relevant alterations in diet, since P. lineatus was not recorded in any stomach of the five species; rather, it was replaced by the shrimp, Macrobrachium amazonicum. Diet overlap was low in all periods. The greatest overlap was obtained in period C for P. squamosissimus and R. vulpinus, due to high consumption of shrimps. There were no significant differences in niche breadth among species. However, the species presented distinct variation patterns in niche breadth. For example, H. aff. malabaricus showed a tendency toward increasing niche over the period, but the other species presented larger niches only during period A. Therefore, it can be concluded that the intensity and duration of the flood pulse influences: (i) the diet composition of piscivores; (ii) the breadth of their niches; and (iii) feeding overlap among species.

Piscivory by Hoplias aff. malabaricus (Bloch, 1794): a question of prey availability?

“…H. aff. malabaricus is an ambush predator, selectively occupying sites with high structural complexity, such as macrophyte banks, where prey abundance tends to be high, thus increasing success of prey capture (Luz- Agostinho et al, 2008), as observed in the present study during the 2006 rainy season. Aquatic macrophytes play an important role in lowland lakes by increasing microhabitat heterogeneity and, consequently, resources for prey (i.e.…”

“…As native predators can decrease Factors such as habitat preference, environmental conditions, prey size and mobility can play a major role on selectivity than prey abundance (Luz- Agostinho et al, 2008;Milani et al, 2010). H. aff.…”

“…Several studies on the biology and importance of the "trahira" to the dynamics of Brazilian environments have been conducted, particularly, in the Rio Paraná Basin (Petry et al, 2010;Novakowski et al, 2007;Luz-Agostinho et al, 2008;Peretti and Andrian, 2004), Amazonas (Galacatos et al, 2004) and Pantanal (Milani et al, 2010;Brandão-Gonçalves et al, 2010). Further, experimental studies on its feeding biology and its role on trophic cascades have also been documented Piana et al, 2006).…”

Effects of the flood regime on the body condition of fish of different trophic guilds in the Upper Paraná River floodplain, Brazil

“…Several studies of the effect of annual variation in water level on the diet of fish in this region have been carried out (Almeida et al, 1997;Hahn et al, 2004;Russo, 2004;Luz-Agostinho et al, 2008). However, studies on the effects of the inter-annual variation of the flood re-ated by the regressions between the logarithms of total weight (Wt) and standard length (Ls), by species.…”

Effects of flooding regime on the feeding activity and body condition of piscivorous fish in the Upper Paraná River floodplain

“…The literature also contains several studies examining the effect of the annual variation in water level on fish diet in the region (Almeida et al, 1997;Hahn et al, 2004;Russo, 2004;Luz-Agostinho et al, 2008) or the effect of regulation and nutrient retention on the food chain length (Hoeinghaus et al, 2008) and carbon flow patterns (Hoeinghaus et al, 2007). Studies on the effects of interannual variations in the flooding regime, especially on a scale involving periods prior to and following the construction of Porto Primavera Reservoir, on aspects related to food intake intensity and fish condition are nonexistent.…”