Analysis of toxic cyanobacterial abundance in selected aquaculture systems and its effect on Oreochromis spp

This study aims to analyse the abundance of toxic cyanobacterial in selected aquaculture systems and its effect on Oreochromis spp. In this study, a total of forty freshwater fish aquaculture ponds were sampled from ten different locations in Perak, Malaysia. To analyse the effects of naturally-occurring microcystins concentration in Perak aquaculture environments on fish, Oreochromis spp. fingerlings were cultured in water treated with cyanobacterial extracts in the laboratory. Study results revealed that the most commonly found cyanobacterial taxa in Perak aquaculture systems was Microcystis spp. During the sampling periods, the majority of the sampled ponds water were under cyanobacterial bloom and contained unsafe concentration of microcystins exceeding 20 μg/L. A combination of temperature and pH was correlated to the proliferation of cyanobacteria and its toxicity in the selected aquaculture ponds. Microcystins accumulated in fish tissues were dependent on the concentration of microcystins in the surrounding water. Despite high microcystins bioaccumulation, this study discovered that microcystin concentrations did not give impacts to the survival and growth of Oreochromis spp. These findings illustrated the potential health risk of toxic cyanobacteria through fish consumption in Malaysia which can be two to three orders of magnitude higher than the tolerable daily intake guideline (0.04 μg MC-LR / kg body weight per day) recommended by World Health Organization. In conclusion, the abundance of toxic cyanobacteria in Malaysia aquaculture systems may cause accumulation by fish at a harmful level. As an implication, this study can serve as a guide on the occurrence of toxic cyanobacteria in our freshwater systems particularly in aquaculture ponds, as well as its potential bioaccumulation in aquatic organisms which may lead to significant health threat to human through food web.