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A rapid and timely response to the impacts of mercury chloride, which is indispensable to the chemical industry, on aquatic organisms is of great significance. Here, we investigated whether the YOLOX (improvements to the YOLO series, forming a new high-performance detector) observation system can be used for the rapid detection of the response of <i>Daphnia magna</i> targets to mercury chloride stress. Thus, we used this system for the real-time tracking and observation of the multidimensional motional behavior of <i>D. magna</i>. The results obtained showed that the average velocity (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">v</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>), average acceleration (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">a</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>), and cumulative travel (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="bold-italic">L</mi></semantics></math></inline-formula>) values of <i>D. magna</i> exposed to mercury chloride stress changed significantly under different exposure times and concentrations. Further, we observed that <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">v</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">a</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="bold-italic">L</mi></semantics></math></inline-formula> values of <i>D. magna</i> could be used as indexes of toxicity response. Analysis also showed evident <i>D. magna</i> inhibition at exposure concentrations of 0.08 and 0.02 mg/L after exposure for 10 and 25 min, respectively. However, under 0.06 and 0.04 mg/L toxic stress, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">v</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="bold-italic">L</mi></semantics></math></inline-formula> showed faster toxic response than <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">a</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>, and overall, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="bold-italic">v</mi><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> was identified as the most sensitive index for the rapid detection of <i>D. magna</i> response to toxicity stress. Therefore, we provide a strategy for tracking the motile behavior of <i>D. magna</i> in response to toxic stress and lay the foundations for the comprehensive screening of toxicity in water based on motile behavior.