Combining a flow-through bioassay system using Daphnia magna with a physicochemical analysis to evaluate the effluent toxicity of the aquaculture farm on the river

The discharge of the effluents from rapidly grown aquaculture farms into the receiving water has led to the pollution of nearby rivers. Therefore, studying the water quality of the rivers and the impact of the aquaculture discharge on the aquatic environment is important. This study evaluated the toxicity of an aquaculture effluent with a Daphnia magna (D. magna) assay in a flow-through system by combining toxicity data and physicochemical analysis. The water samples were analyzed for physicochemical characteristics, total metals, pesticides, and for immobilization with D. magna. The LC50 post 24, 48, 72, and 96 h of exposure was adopted as the endpoint and estimated statistically by the Probit method. The results showed that all these physicochemical parameters and total metals meet Environmental Protection Agency standards for the effluents and no pesticides were detected. The LC50 value (mg/L) of the samples was 0.731 after 24 h while it dropped to 0.527, 0.486, and 0.367 at 48, 72, and 96 h exposure intervals, respectively. Regression analysis showed significant relationships between LC50 vs. concentration and time exposure. That is the higher the concentration and the longer exposure time to D. magna, the higher the toxicity. The present study showed that aquaculture effluent has toxicity to biota even if they apparently met standards for effluent discharge limits since aquaculture effluent is complex mixtures and its individual components cannot be routinely measured. It could be concluded combining a bioassay with a physicochemical analysis is a useful tool to monitor the quality of water bodies that protect aquatic lives.