Resilience assessment of a biological early warning system based on the locomotor behavior of zebrafish (Danio rerio).

With the development of new tools such as biological early warning systems, it becomes extremely important to test their reliability and detection capability. This work aimed at testing the sturdiness of a video tracking system by determining whether the detection capability does not deteriorate over time, after successive exposures of the zebrafish to three different toxicants, namely sodium hypochlorite, bisphenol A, and ethanol. Zebrafish were exposed to the three tested compounds separately (one fish, one toxicant) once a day, for 1 h and 30 m over 9 days, to 9 % of the 96 h LC50 of the respective toxicant. The behavior analysis was based on nine movement descriptor parameters of the fish, namely: angular velocity; linear velocity; spatial dispersion; linear acceleration; and angular acceleration. A statistical method was developed using self-organizing map (SOM), correspondence analysis, and linear and orthogonal multiple regression models. The results indicated that the system was able to successfully detect the three toxicants. With ethanol, the detection capability was maintained, but in the case of the sodium hypochlorite and bisphenol A, a deterioration of the detection capability occurred over the 9 days. This effect may be due to the induction of detoxification mechanisms and physiological acclimation, or due to the accumulation of adverse effects caused by the repeated exposure to the toxicants. Future works, especially those focusing on the application of similar early warning systems in real-world scenarios, should regularly exchange the sentinel organisms, to avoid degradation of the detection capability, as verified with two of the three tested compounds.