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Data of Thesis


Author: Raquel Moraes Soares

Title:.Accumulation, depuration and effects of mycrocystins (cyanobacteria hepatotoxins) in Tilapia rendalli (Cichlidae)

Year: 1999.    Full text (in Portuguese)


The occurrence of blooms of Microcystis aeruginosa in several water bodies has been frequently reported. This cyanobacteria species is able to produce microcystins hepatotoxic heptapeptide), which can cause serious damage on the aquatic biota and mammalian. The effects of the toxic cyanobacteria M aeruginosa in fish are relevant due to the ecological, economic and social importance of these organisms usually consumed as human food. This work studied the process of accumulation and depuration of microcystins in Tilapia rendalli and the effects of these toxins on the growth of this fish. Three experiments with juveniles maintained in lab conditions were done. In the first one each fish received, during 15 days, fish food plus toxic cells of M aeruginosa (20.4µg of microcystins per day). In the following 15 days, the organisms were feed without toxic cells. Four fishes were harvested every 3 days and feces were collected for microcystins analyses. In the second experiment, fishes were feed, only with toxic cells of M aeruginosa (I 4,6J.1g of microcystins/day/fish) during 28 days. In the third experiment, fishes were feed with fish food plus toxic cells previously lised (29,2J.1g of microcystins/day/fish), during 6 weeks. In these two last experiments, fishes were harvested every 7 days, and the biometric parameters were annotated. The microcystin concentration in the liver, muscle and fasces were determined by ELISA immunoassays. In the first experiment the highest concentration of microcystins in the liver tissue was observed on the 6th.day (0,6J.1g.g-1), while in the muscle it occurred during depuration period (24th. day 0,05J.1g.g-1). It suggested a possible transference of microcystins from the liver to the muscle. Almost 50% of the toxins were released through the fasces during the depuration period. In the second experiment, the nourishment only with toxic cells could have caused the accumulation of higher microcystin concentrations •than in the other experiments. In the third experiment, the toxins were released by cellular lise and the uptake of these toxins seemed to be different. In the liver, the highest concentration was observed on the last day (1,7J.1g.g-1). During this experiment a decrease in body weight was verified in the intoxicated individuals. This study showed us that Tilapia rendalli when consuming M aeruginosa cells and microcystins in concentrations usually found during blooms occurrence can accumulate these toxins above the tolerable limit for human consumption. This fact can be a serious risk for aquatic ecosystem and public health.