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

Abstract

The increase in abundance of small-sized fishes is common after a reservoir is formed. There is an increase in the consumption of fish, from typically piscivorous fish to opportunistic species that take advantage of abundant resources. This study aims to evaluate the effects of diet changes induced by damming on the feeding activity and condition factor of typically piscivorous (Hoplias aff. malabaricus and Oligosarcus longirostris) and opportunistic (Astyanax lacustris (ex Astyanax altiparanae) and Pimelodus britskii). Sampling was conducted before and after the impoundment in the Iguaçu River in the region of Salto Caxias, Paraná State, Brazil. Stomach contents were analysed by the volumetric method. Feeding activity and body condition were inferred by the mean stomach repletion index and the mean condition factor. Typically piscivorous species presented a general tendency of decreased feeding activity and increased condition factor, while opportunistic species, presented a decrease in condition and feeding activity in the most affected sites. The increase in the condition factor of piscivorous fish suggests that these species benefit by the increased abundance of small size prey fish. Some opportunist species that do not have adjustments for the piscivorous diet, regardless of the intensity of consumption and resource availability, can suffer negative reflex when adopting a piscivorous diet.O aumento na abundância de peixes de pequeno porte é comum logo após a formação de um reservatório, levando a um aumento no consumo de peixes, tanto por peixes piscívoros como oportunistas que se aproveitam do recurso abundante. Esse estudo visa avaliar os efeitos da mudança de dieta induzida pelo represamento na atividade alimentar e condição nutricional, tanto de espécies piscívoras (Hoplias aff. malabaricus e Oligosarcus longirostris) quanto de espécies oportunistas (Astyanax lacustris (ex Astyanax altiparanae) e Pimelodus britskii). Para tanto, foram realizadas amostragens nas fases pré e pós-represamento no rio Iguaçu na região de Salto Caxias, Paraná, Brasil. Os conteúdos estomacais foram avaliados pelo método volumétrico. A atividade alimentar foi determinada pelo índice de repleção estomacal e a condição nutricional através do fator de condição relativo. As espécies tipicamente piscívoras apresentaram, em geral, incremento no fator de condição e queda na atividade alimentar e a espécie mais oportunista apresentou queda no fator de condição e índice de repleção nas regiões mais afetadas pelo represamento. O aumento no fator de condição de espécies piscívoras sugere que estas se beneficiam pelo aumento de abundância das espécies de pequeno porte. Enquanto espécies que não possuem adaptações para uma dieta piscívora, independente da intensidade de consumo e disponibilidade desse recurso, podem sofrer reflexos negativos em sua condição nutricional, em detrimento da ausência de pré-adaptações à piscivoria.

Fish trophic guild responses to damming: Variations in abundance and biomass

“…Thus, the observed decrease in guild abundance in the impacted site may be related to migrating fish searching for ideal environmental conditions. As another plausible hypothesis, increased levels of predation pressure resulting from increased water transparency (Chacin & Stallings, ; Pereira et al, ; Shoup & Lane, ) should be able to change several guilds, as all guilds are subject to predation.…”

“…As another plausible hypothesis, increased levels of predation pressure resulting from increased water transparency (Chacin & Stallings, 2016;Pereira et al, 2016;Shoup & Lane, 2015) should be able to change several guilds, as all guilds are subject to predation.…”

Temporal fish community responses to two cascade run‐of‐river dams in the Madeira River, Amazon basin

“…Otherwise, blocking their migration route along Madeira River and suppressing or reducing the effects of the seasonal flooding could lead to local depletion or extirpation of populations of migratory fishes in the long run (Duponchelle et al, 2016;Kuussaari et al, 2009;Porcher & Travade, 1992). Still, some species that were previously abundant in the rapids stretch of tributaries, especially piscivores such as Acestrorhynchus spp., have become scarce in the reservoirs, suggesting low adaptability to the new conditions and possibly local changes in trophic dynamics (but see Pereira, Agostinho, & Delariva, 2016).…”

Population structure, size at first sexual maturity, and feeding ecology of Conodon nobilis (Actinopterygii: Perciformes: Haemulidae) from the coasts of Pernambuco, north-eastern Brazil

“…Trawls mainly target demersal organisms (McHugh et al 2017) and species that forage near the bottom (Pombo et al 2014), such as C. nobilis, which is directly affected by such trawling activity. The feeding intensity, described as the fullness index (FI), may be greatly influenced by the availability and type of prey, length range of the predator, reproductive season, and daily variation (Pereira et al 2016, Perelman et al 2017. In the presently reported study, high FI values were found, indicating an intense use of the environment as a feeding area.…”