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

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

Is There a Relationship between Fish Cannibalism and Latitude or Species Richness?

<div><p>Cannibalism has been commonly observed in fish from northern and alpine regions and less frequently reported for subtropical and tropical fish in more diverse communities. Assuming all else being equal, cannibalism should be more common in communities with lower species richness because the probability of encountering conspecific versus heterospecific prey would be higher. A global dataset was compiled to determine if cannibalism occurrence is associated with species richness and latitude. Cannibalism occurrence, local species richness and latitude were recorded for 4,100 populations of 2,314 teleost fish species. Relationships between cannibalism, species richness and latitude were evaluated using generalized linear mixed models. Species richness was an important predictor of cannibalism, with occurrences more frequently reported for assemblages containing fewer species. Cannibalism was positively related with latitude for both marine and freshwater ecosystems in the Northern Hemisphere, but not in the Southern Hemisphere. The regression slope for the relationship was steeper for freshwater than marine fishes. In general, cannibalism is more frequent in communities with lower species richness, and the relationship between cannibalism and latitude is stronger in the Northern Hemisphere. In the Southern Hemisphere, weaker latitudinal gradients of fish species richness may account for the weak relationship between cannibalism and latitude. Cannibalism may be more common in freshwater than marine systems because freshwater habitats tend to be smaller and more closed to dispersal. Cannibalism should have greatest potential to influence fish population dynamics in freshwater systems at high northern latitudes.</p></div

Predicted influence of prey species diversity on probability of prey encounter rates and cannibalism.

<p>In a species-rich assemblage (A), low relative abundance of conspecific prey (red curves) results in low rates of encounter with conspecifics relative to heterospecific prey (black curves) and a low rate of cannibalism. In a species-poor assemblage (B), conspecific prey comprise a greater percentage of available prey, and encounter rates with conspecifics and cannibalism would be higher. Curves represent size frequency distributions of various prey. Heavy black horizontal line represents the range of prey sizes consumed by the predator. Pie charts represent dietary proportions of conspecific (red area) and heterospecific prey (white area).</p

The global distribution of cannibalism occurrence based on a survey of 1,270 literature sources.

<p>Points represent the geographical coordinates of each study included in the literature review. Black dots represent studies reporting cannibalism and open dots denote absence of reported cannibalism. To avoid overlapping points, 234 coordinates were not plotted, including 134 for absence and 100 for presence of cannibalism.</p

Generalized linear mixed models (GLMM) for the relationship between cannibalism occurrence and latitude.

<p>Freshwater (top figures) and marine (bottom figures) realm in the Northern (left figures) and Southern hemisphere (right figures). Lines are the predicted cannibalism probability along latitudinal gradients according to each model. Shaded areas around probabilities lines represent the 95% CI. Dots are observed data for absence (0) or presence (1) of cannibalism according to fish species richness.</p

Generalized linear mixed models (GLMM) for the relationship between cannibalism occurrences and freshwater fish richness.

<p>Northern hemisphere (left side) and southern hemisphere (right side). Lines are the predicted cannibalism probability along richness gradients according to each model. Shaded areas around probabilities lines represent the 95% CI. Dots are observed data for absence (0) or presence (1) of cannibalism according to fish species richness.</p

Parameter estimation of the best models (GLMM with delta AIC lower than 2) predicting occurrence of cannibalism for both freshwater and marine realm in Northern and Southern hemispheres.

<p>Parameter estimation of the best models (GLMM with delta AIC lower than 2) predicting occurrence of cannibalism for both freshwater and marine realm in Northern and Southern hemispheres.</p

Longitudinal gradient in limnological variables in the Upper Paraná River: a brief description and the importance of undammed tributaries

<div><p> Abstract Aim: Describe the limnological pattern in a longitudinal gradient in the Paraná River, a highly dammed river, in a stretch localized between two dams, but rich in undammed tributaries. Methods Twelve transects in the longitudinal gradient of the Paraná River were sampled, with the first transect being placed right after Porto Primavera dam, and the last one in the lotic region of the Itaipu dam. In each of these transects, water transparency, electrical conductivity, pH, total nitrogen and total phosphorous were analyzed. Results In those regions nearer Porto Primavera dam it was observed high values of water transparency and low values of nitrogen and phosphorous. The values of water transparency decreased and the values of nitrogen and phosphorous increased as the distance from Porto Primavera dam increased. Because the new tributaries connect to the Paraná River, with the sites farer from Porto Primavera dam presenting values similar to those prior its construction. Conclusions Increase in the nutrients concentration and changes in ecological integrity are probably due to the presence of the undammed tributaries. They are originate in different river basins and therefore contribute to the Paraná River in distinct manners. Results presented here are an indicative of the fundamental importance of undammed tributaries in mitigating damming negative impacts in extremely dammed rivers and highlight the importance of keeping such tributaries free of dams.</p></div