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

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.

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

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. (AU)

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. (AU)

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

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.