Toxic Assessment of Cadmium Based on Online Swimming Behavior and the Continuous AChE Activity in the Gill of Zebrafish ( Danio rerio )

The cadmium (Cd) contamination in the aquatic environment has attracted more and more attention due to its toxicity characteristics, e.g., accumulation in the environment, non-degradability, and the potential threat to the ecosystem. In this research, in order to illustrate the potential threat of heavy metal Cd to aquatic organisms, the online swimming behavior and the continuous acetylcholinesterase (AChE) activity in the gill of Zebrafish ( Danio rerio ) in 48 h exposure of cadmium chloride (CdCl 2 ) (4.26 mg/L (0.1 TU, toxic unit), 42.6 mg/L (1.0 TU), and 85.2 mg/L (2.0 TU)) are investigated. The behavior responses of D. rerio based on behavior strength (BS) have obvious dose-effect relationship, and lower BS values could be observed in the dark period at 13–21 h and 37–45 h in all treatments. The circadian rhythm could be observed even in all treatments (0.1, 1.0, and 2.0 TU), and the rhythm was disrupted with 1.0 TU at the end of the experiment whereas the lower (0.1 TU) and higher (2.0 TU) levels showed clear rhythms. These results suggested that the online BS values could illustrate the toxicity of CdCl 2 directly. The AChE activity in the gill is strongly inhibited by CdCl 2 based on the continuous sample results during 48 h exposure. The cross-correlation results using DCCA show a high correlation ( r > 0.5) with extreme significance ( p < 0.01), which suggest that the exposure in CdCl 2 can affect the AChE activity of D. rerio , and then damage the transduction signal due to neurotoxicity, which may induce decrease of swimming behavior, loss of coordination, and other kinds of behavior changes.