Water quality and zooplankton in tanks with larvae of Brycon Orbignyanus (Valenciennes, 1949).

Due to the importance of water variables conditions and available food in the development and survival of fish larvae, the current research evaluates the effects of two different food treatments (ration + zooplankton and only zooplankton) and water quality in tanks with Brycon orbignyanus larvae. Total water transparency (45 cm) has been mainly associated with short residence time, continuous water flow and shallowness. Dissolved oxygen ranged between 1.32 and 7.00 mg.L(-1) in tanks with ration + zooplankton and between 1.82 and 7.60 mg.L(-1) in tanks with only zooplankton treatments. Nutrients were directly affected by the addition of ration in water, with the exception of nitrite. Ten Rotifera species were found represented by high densities, ranging between 8.7 x 10(5) and 1.3 x 10(6) org.m(-3), throughout the experimental period (January to March/1996). Cladocera had the lowest density in the four tanks under analysis and ranged between 4.7 x 10(4) and 2.1 x 10(5) org.m(-3) for the six species. Diaphanosoma birgei has been classified as the most frequent species. Since ration + zooplankton produced better larvae yield, this treatment is recommended for Brycon orbignyanus larvae.

Water quality and zooplankton in tanks with larvae of Brycon Orbignyanus (Valenciennes, 1949)

Due to the importance of water variables conditions and available food in the development and survival of fish larvae, the current research evaluates the effects of two different food treatments (ration + zooplankton and only zooplankton) and water quality in tanks with Brycon orbignyanus larvae. Total water transparency (45 cm) has been mainly associated with short residence time, continuous water flow and shallowness. Dissolved oxygen ranged between 1.32 and 7.00 mg.L-1 in tanks with ration + zooplankton and between 1.82 and 7.60 mg.L-1 in tanks with only zooplankton treatments. Nutrients were directly affected by the addition of ration in water, with the exception of nitrite. Ten Rotifera species were found represented by high densities, ranging between 8.7 x 10(5) and 1.3 x 10(6) org.m-3, throughout the experimental period (January to March/1996). Cladocera had the lowest density in the four tanks under analysis and ranged between 4.7 x 10(4) and 2.1 x 10(5) org.m-3 for the six species. Diaphanosoma birgei has been classified as the most frequent species. Since ration + zooplankton produced better larvae yield, this treatment is recommended for Brycon orbignyanus larvae.

Devido à importância das condições das variáveis da água e do alimento disponível no desenvolvimento e sobrevivência das larvas de peixes, o objetivo deste estudo foi avaliar o efeito do uso de dois tratamentos alimentares (ração + zooplâncton e somente zooplâncton) e a qualidade da água, em tanques de larvicultura de Brycon orbignyanus. A transparência total da água (45 cm) esteve associada principalmente ao curto tempo de residência, fluxo contínuo e baixa profundidade. As concentrações de oxigênio dissolvido variaram de 1,32 a 7,00 mg.L-1 no tratamento contendo ração + zooplâncton, e de 1,82 a 7,60 mg.L-1 no tratamento contendo somente zooplâncton. Os nutrientes foram diretamente influenciados pela adição de ração no meio com exceção do nitrito. Rotifera apresentou a maior densidade, variando ao longo do período experimental de 8,7 x 10(5) a 1,3 x 10(6) org.m-3 entre os quatro tanques estudados, num total de dez espécies. A menor densidade foi observada para Cladocera, variando de 4,7 x 10(4) a 2,1 x 10(5) org.m-3 num total de seis espécies encontradas, sendo Diaphanosoma birgei a única espécie classificada como muito freqüente. O uso de ração junto com zooplâncton proporcionou melhor rendimento para larvas de B. orbignyanus.