Diel vertical migration and spatial overlap between fish larvae and zooplankton in two tropical lakes, Brazil / Migração vertical diária e sobreposição espacial entre larvas de peixes e zooplâncton em dois lagos tropicais, Brasil

The effect of fish larvae on the diel vertical migration of the zooplankton community was investigated in two tropical lakes, Finado Raimundo and Pintado lakes, Mato Grosso do Sul State, Brazil. Nocturnal and diurnal samplings were conducted in the limnetic region of each lake for 10 consecutive months from April 2008 to January 2009. The zooplankton community presented a wide range of responses to the predation pressure exerted by fish larvae in both environments, while fish larvae showed a typical pattern of normal diel vertical migration. Our results also demonstrated that the diel vertical migration is an important behaviour to avoid predation, since it reduces the spatial overlap between prey and potential predator, thus supporting the hypothesis that vertical migration is a defence mechanism against predation.

O efeito de larvas de peixes sobre a distribuição vertical dia-noite da comunidade zooplanctônica foi investigada em duas lagoas tropicais, lagoa Finado Raimundo e Pintado, Mato Grosso do Sul, Brasil. Foram realizadas amostragens noturnas e diurnas na região limnética de cada lagoa durante um período de 10 meses consecutivos, entre abril de 2008 a janeiro de 2009. A comunidade zooplanctônica apresentou uma variada gama de respostas à pressão de predação exercida pelas larvas de peixes nos dois ambientes, enquanto que as larvas de peixes exibiram um padrão típico de migração vertical diária normal. Os resultados mostraram ainda, que a migração vertical diária é um comportamento importante para evitar a predação, uma vez que diminuiu a sobreposição espacial entre presa e seu predador em potencial, dando suporte a hipótese de que a migração vertical é um mecanismo de defesa contra a predação.

Spatial and temporal distribution of larvae and juveniles of Hoplias aff. malabaricus (Characiformes, Erythrinidae) in the upper Paraná river floodplain, Brazil

Spatial and temporal distribution of larvae and juveniles of trahira, Hoplias aff. malabaricus (Erythrinidae), and their relationship with environmental parameters in the Upper Paraná River floodplain were analyzed. Sampling of larvae and juveniles of H. aff. malabaricus has been conducted during the period from November 1991 through February 1995, with 42 sampling stations distributed in four sub-areas: Ivinhema I, Ivinhema II, Baía, and Paraná. During the same period, data were obtained for water temperature, dissolved oxygen, pH, electrical conductivity, river level, precipitation index, and photoperiod. The largest catches of larvae were in the Ivinhema I sub-area (47.06 percent), and of juveniles in the Paraná sub-area (54.55 percent). Larvae and juveniles were caught from October to February. Larvae were mainly collected at night and in all types of environments sampled (lotic, semi-lotic, and lentic). Principal Component Analysis of the environmental parameters and larval density showed that the largest catches were obtained in dry season months, with low values for temperature, electrical conductivity, river level, and photoperiod, and with high concentrations of dissolved oxygen and pH. This reproductive strategy may minimizes predation and maximizes food utilization, as it enables the fish to reach advanced developmental stages, while most other species are spawning

Spatial and temporal distribution of larvae and juveniles of Hoplias aff. malabaricus (Characiformes, Erythrinidae) in the Upper Paraná River floodplain, Brazil

Spatial and temporal distribution of larvae and juveniles of trahira, Hoplias aff. malabaricus (Erythrinidae), and their relationship with environmental parameters in the Upper Paraná River floodplain were analyzed. Sampling of larvae and juveniles of H. aff. malabaricus has been conducted during the period from November 1991 through February 1995, with 42 sampling stations distributed in four sub-areas: Ivinhema I, Ivinhema II, Baía, and Paraná. During the same period, data were obtained for water temperature, dissolved oxygen, pH, electrical conductivity, river level, precipitation index, and photoperiod. The largest catches of larvae were in the Ivinhema I sub-area (47.06%), and of juveniles in the Paraná sub-area (54.55%). Larvae and juveniles were caught from October to February. Larvae were mainly collected at night and in all types of environments sampled (lotic, semi-lotic, and lentic). Principal Component Analysis of the environmental parameters and larval density showed that the largest catches were obtained in dry season months, with low values for temperature, electrical conductivity, river level, and photoperiod, and with high concentrations of dissolved oxygen and pH. This reproductive strategy may minimizes predation and maximizes food utilization, as it enables the fish to reach advanced developmental stages, while most other species are spawning.

Analisou-se a distribuição espaço-temporal de larvas e juvenis de Hoplias aff. malabaricus (Erythrinidae) na planície de inundação do alto rio Paraná e suas relações com algumas variáveis ambientais, verificando-se os habitats preferenciais para a reprodução e desenvolvimento inicial. As amostragens foram divididas em quatro fases realizadas durante o período de novembro de 1991 a fevereiro de 1995, sendo estabelecidas 42 estações de coleta distribuídas em 4 subáreas (Ivinhema I, Ivinhema II, Baía e Paraná). As coletas foram realizadas na coluna de água e na vegetação aquática marginal. Durante o período foram obtidos dados de temperatura da água, oxigênio dissolvido, pH, condutividade elétrica, nível fluviométrico, índice pluviométrico e fotoperíodo. As maiores capturas de larvas foram verificadas na subárea Ivinhema I (47,06%) e, de juvenis, na subárea Paraná (54,55%). As larvas foram encontradas entre outubro e fevereiro em todas as subáreas, já os juvenis foram encontrados até abril. As larvas foram capturadas principalmente durante o período noturno em todos os tipos de ambientes amostrados (lótico, semilótico e lêntico). A Análise de Componentes Principais, aplicada entre as variáveis ambientais e a densidade de larvas, revelou que as maiores capturas são obtidas em meses em que predominam baixos valores de temperatura, condutividade elétrica, nível fluviométrico e fotoperíodo e elevadas concentrações de oxigênio dissolvido e de pH, ou seja, em meses de seca. Esta estratégia reprodutiva minimiza a predação e maximiza o aproveitamento alimentar, uma vez que lhe permite alcançar estágios avançados enquanto a maioria das espécies está desovando.