The Toxic Effect Of Microcystis Aerugrinosa On Macrobrachium Rosenbergii And Daphnia Magna

The frequent occurrence of heavy cyanobacteria blooms, of which the toxic blue algae Microcystis aerugrinosa as the most common species, in eutrophic fresh water has been a worldwide problem, which leads to the possibility of adverse effects on many aquatic organisms due to the toxic microcystins produced and released by the cyanobacteria blooms and deteriorated water quality factors. The effect of Microcystis on aquatic organisms especially zooplankton and shrimps have been broadly reported at home and abroad. In this paper, we detected the microcystin in Microcystis aeruginosa by HPLC-MS. Then after the Daphnia magna and Macrobrachium rosenbergii acute toxicity experiment, we found the microcystin had obvious toxicity influence on these two species. In addition, we detected Microcystin in Daphnia magna in the toxin accumulation experiment. The comprehensive analysis of the Microcystis hazards contributed for study of the toxicity of microcystins in the future.The microcystins (MCs) in Microcystis aeruginosa, and Daphnia magna exposed to M. aeruginosa, were analyzed by HPLC-MS, and the effects of M. aeruginosa on D. magna were investigated. When D. magna was exposed to M. aeruginosa for more than 2 h, MC-LR was detected. When exposed to 1.5×10⁶, 3×10⁶, 0.75×10⁷, and 1.5×10⁷cells/ml of M. aeruginosa for 96 h, average survival rate of D. magna for treatments were 23.33, 33.33, 13.33, 16.67%, respectively, which were significantly lower than the average 100% survival in the control group (P<0.05). The adverse effects of M. aeruginosa on body length, time for the first brood, brood numbers, gross fecundity, lifespan, and population growth of D. magna were density-dependent. These results suggest that the occurrence of M. aeruginosa blooms could strongly inhibit the population growth of D. magna through depression of survival, individual growth and gross fecundity. In the most serious situations, M. aeruginosa blooms could undermine the food web by eliminating filter-feeding zooplankton, which would destroy the ecological balance of aquaculture water bodies.In the study of M. aerugrinosa to M. rosenbergii, three independent experiments were conducted to investigate the impacts of M. aerugrinosa on the survival, growth of M.rosenbergii. (1)Juvenile prawns M.rosenbergii (10.331.44mm in body length) were exposed to different concentrations of M. aerugrinosa (0, 1 106, 5 106, 10 106, 20 106, 30 106cell/ml). The results showed that M. aeruginosa had negative effect on the survival of the juvenile shrimp and the lethal concentration 50 (LD₅₀) of M. aeruginosa at 144 and 168h were 36.08 106 and 28.81 106cell/ml respectively. (2)When prawns(8.10.82mm in body length) were exposed to M. aerugrinosa at 0, 2 106, 10106cell/ml for 80d, the growth rate of the prawns in M. aerugrinosa cultures at 2106 and 10 106cell/ml were slower comparing to the control(P<0.05). (3) M.rosenbergii were stocked to different concentrations of M. aerugrinosa for 28d and tissues from the prawns (hepatopancreas, muscle, eyestalk, heart, stomach, intestine and gill) were sampled and detected using HPLC/MS method to evaluate the accumulation of microcystins which is toxic secondary metabolites of M. aeruginosa. The result showed no accumulation of MCs in those tissues, which indicated that the toxic MCs were not the cause of death to shrimps. Further studies are needed to investigate the mechanism of lethal effect of M. aerugrinosa on juvenile prawn M.rosenbergii.