First monitoring of cyanobacteria and cyanotoxins in freshwater from fish farms in Rondônia state, Brazil.

The main aimed of this study was to evaluate the physicochemical parameters, abundance and density of cyanobacteria, determine their blooms and the ecotoxicological risk of their cyanotoxins in fish ponds water. This study was conducted out in 20 fish farms in Rondônia state (Brazilian Amazon), samplings were carried out in the rainy and dry seasons. The experiment was developed in a completely randomized factorial design 20 × 3 x 3 (20 fish farms, 3 ponds and 3 replications). Regarding the composition of qualitative samples, horizontal and vertical hauls were carried out on the water surface, quantitative samples was obtained using a plankton net (50 µm mesh opening). Meanwhile, with the use of a multiparametric probe, physicochemical analyzes in fish ponds water were carried out. Furthermore, the cyanobacteria found were classified taxonomically and its blooms were recorded. Finally, blood was collected from 60 Colossoma macropomum. Concerning the higher averages in the rainy season 6.13 mg L⁻1 of dissolved oxygen, 40.02 cm of transparency, 0.35 NO31⁻ of nitrate, 0.15 NO21⁻ of nitrite, 44.55 mg L⁻1 CaCO3 of alkalinity and 50.10 mg L⁻1 CaCO3 of hardness, while higher averages of pH, phosphate and phosphorus were found in the dry season. A total of 15 families and 29 species of cyanobacteria were identified in the different seasons. The families that showed the highest densities (rainy and dry seasons) were Microcystaceae (356 and 760 cells mL⁻1), Leptolyngbyaceae (126 and 287 cells mL⁻1) and Microcoleaceae (111 and 405 cells mL⁻1). The species that showed the highest densities were Microcystis aeruginosa (356 and 697 cells mL⁻1), Planktolyngbya limnetica (98 and 257 cells mL⁻1) and Planktothrix sp. (111 and 239 cells mL⁻1). There were significant Pearson's correlations (r > 0.85; p < 0.05) between family abundances and cyanotoxin volume between physicochemical water variables and seasonality. A total of 20 cyanobacteria blooms were recorded, all of which in the dry season showed an ecotoxicological risk. Concerning the assessment mutagenicity in fish blood cells, a total of 78 abnormalities per slide were observed. In the dry season, the expected volume of cyanotoxins in the ponds from fish farms F1 and F4 were above the quantification limit (>QL). Abundance and density of cyanobacteria and their blooms and cyanotoxins can be used as bioindicators of eutrophication and/or water quality and ecotoxicological risk in fish ponds.