Energy sources for detritivorous fishes in the Amazon.

Detritivorous fishes form an important part of the ichthyomass in the Amazon basin. Most of these fishes are contained in the orders Characiformes and Siluriformes (catfishes). The Characiformes constitute more than 30% of the total fish yield in the Amazon basin, whereas the catfishes are of minor importance. Stable isotope data indicate that Characiformes species receive most of their carbon through food chains originating with phytoplankton, while the Siluriformes receive a significant part of their energy from other plant sources.

Transportation of juvenile tambaqui (Colossoma macropomum) in a closed system.

The objective of this study was to investigate the effect of density, duration and the use of additives to the water during the transportation of juvenile tambaqui (Colossoma macropomum) and use of this data to establish a safe transportation protocol for the species. The tested products and dosages were: salt (1000, 2000 and 3000 mg/L), gypsum (100, 300 and 500 mg/L) and benzocaine (10, 20 and 30 mg/L). Fish were transported in closed systems (plastic bag) at different densities and time periods of up to 24 h. Fish survival (FS) and water quality parameters were monitored immediately after transportation. The remaining fish were kept in floating cages in order to evaluate mortality which occurred up to 96 h after transportation (S96). The best fish density, additives dosages and time period of the transportation was estimated with a general linear model. The effect of the condition factor on FS and S96 was also evaluated. As expected, FS and S96 were significantly related to time and density. FS but not S96, were also were significantly related to treatment. FS with gypsum treatment was not different from controls and FS with table salt and benzocaine treatments were significantly reduced. The condition factor was not related to either FS or S96. FS was inversely correlated with carbon dioxide concentration. It was concluded that the additives did not improve fish transportation survival. Linear models were developed to predict the best transportation densities as a function of time.

Diel variation of larval fish abundance in the Amazon and Rio Negro.

Many streams and large rivers present higher ichthyoplankton densities at night. However, in some rivers this does not occur and larvae are equally abundant during the day. Larval drift diel variation is an important information for planning sampling programs for evaluating larval distribution and production. The aim of this study was to test whether the abundance of larval fish was different at either period. We tested it by comparing day and night densities of characiform, clupeiform and siluriform larvae during five years in the Amazon and one year in Rio Negro. We found that larvae of three species of characiform and larvae of siluriform were equally abundant during day and night in the Amazon. Conversely, the catch of Pellona spp. larvae was significantly higher during the day. In Rio Negro, however, larval abundance was higher during the night. These results imply that day samplings estimate adequately the abundance of these characiform and siluriform larvae in the Amazon, but not Pellona larvae. Evaluations of larved densities of Rio Negro will have to consider night sampling.

Transportation of juvenile tambaqui (Colossoma macropomum) in a closed system

O objetivo deste estudo foi investigar o efeito da densidade, duração e do uso de aditivos na água durante o transporte de juvenis de tambaqui (Colossoma macropomum) e usar estes resultados para estabelecer um protocolo seguro de transporte para esta espécie. Os produtos testados e suas doses foram: sal de mesa (1000, 2000 e 3000 mg/L), gesso (100, 300 e 500 mg/L) e benzocaína (10, 20 e 30 mg/L). Os peixes foram transportados em sistema fechado (saco plástico) em diferentes densidades e por diferentes tempos por até 24 h de transporte. A sobrevivência e os parâmetros de qualidade da água foram monitorados imediatamente após o transporte. Os peixes que sobreviveram ao transporte foram colocados em tanques-rede para avaliar a mortalidade após 96 h. A melhor densidade, tempo de transporte e aditivo foram estimados por modelo linear geral. O efeito do fator de condição na sobrevivência após o transporte e na sobrevivência de 96 h também foi avaliado. Como esperado, a sobrevivência após o transporte e a sobrevivência de 96 h foram significativamente correlacionados com o tempo e a densidade. A sobrevivência após o transporte, mas não a sobrevivência de 96 h, também tem correlação com os aditivos testados. A sobrevivência após o transporte é significativamente igual para o tratamento controle e para os tratamentos que receberam gesso e significativamente menor para os tratamentos que receberam sal e benzocaína. O fator de condição não tem correlação com a sobrevivência após o transporte e a sobrevivência de 96 h. É conclusivo que os aditivos testados não melhoram a sobrevivência de juvenis de tambaqui após o transporte. Modelos lineares foram desenvolvidos para predizer a melhor densidade de transporte em função do tempo.

Diel variation of larval fish abundance in the Amazon and Rio Negro

Many streams and large rivers present higher ichthyoplankton densities at night. However, in some rivers this does not occur and larvae are equally abundant during the day. Larval drift diel variation is an important information for planning sampling programs for evaluating larval distribution and production. The aim of this study was to test whether the abundance of larval fish was different at either period. We tested it by comparing day and night densities of characiform, clupeiform and siluriform larvae during five years in the Amazon and one year in Rio Negro. We found that larvae of three species of characiform and larvae of siluriform were equally abundant during day and night in the Amazon. Conversely, the catch of Pellona spp. larvae was significantly higher during the day. In Rio Negro, however, larval abundance was higher during the night. These results imply that day samplings estimate adequately the abundance of these characiform and siluriform larvae in the Amazon, but not Pellona larvae. Evaluations of larved densities of Rio Negro will have to consider night sampling