Accumulation and depuration of microcystins (cyanobacteria hepatotoxins) in Tilapia rendalli (Cichlidae) under laboratory conditions

In order to understand accumulation and depuration of microcystins (MCYSTs) in Tilapia rendalli, three experiments with juveniles were done. The experiments simulated the fish diet during a Microcystis aeruginosa bloom in three different situations. In the first one each fish received daily, during 15 days, fish food plus toxic cells of M. aeruginosa (20.4 micrograms MCYSTs fish -1 day -1). In the following 15 days they were fed without toxic cells. In the second experiment, fish were fed only with toxic cells during 28 days (14.6 micrograms MCYSTs fish -1 day -1) and in the third experiment, during 42 days, fish were fed with fish food plus toxic cells (29.2 micrograms MCYSTs fish -1 day -1) previously disrupted (to simulate a senescent bloom). MCYSTs analyses were done by enzyme-linked immunosorbent assay (ELISA) in liver and muscle samples in all experiments and in faeces in the first one (only in the depuration period). The results demonstrated different profiles of MCYSTs accumulation in liver and muscle of T. rendalli. Comparing the experiments, the highest MCYSTs accumulation in the liver (2.8 micrograms g -1) occurred in the second one, where fish had only toxic cells as feeding source. In the first experiment, the highest MCYSTs accumulation in liver (0.6 micrograms MCYSTs g -1) was observed during the accumulation period, while in muscle, interestingly, the highest concentration (0.05 micrograms MCYSTs g -1) occurred in the depuration period. In this same period, it was also observed elimination of toxins through faeces. The second and third experiments showed almost the same average concentrations in tissues although fish have received more MCYSTs in third one. With respect to implications of the fish comsumption, MCYSTs accumulation in muscle of T. rendalli in all three experiments reached concentrations that would represent an intake of these toxins above the tolerable limit for humans and these results confirmed our previous observations from a field study. In conclusion, in this study it was observed that T. rendalli is able to accumulate MCYSTs and the availability of other feeding sources, besides toxic cells, probably interferes with the accumulation rate. Therefore, the occurrence of toxic cyanobacterial blooms produncing MCYSTs in aquaculture ponds could represent a risk to the quality of fish to the consumers.