Research On Early-warning Of Water Quality By Monitoring Behavioral Responses Of Zebrafish (Danio Rerio) To Acute Stress

Nowadays, water pollution problem become more serious, at the same time,emergent water pollution accidents have happened more frequently. It not onlyundermined the balance of the ecosystem but also posed a serious threat to human life.Therefore, it has become a hotspot to achieve real-time monitoring of water pollution.This study based on behavior change of zebrafish (Daino rerio) group, which wasrecorded by video tracking technology, simulated and summarized the laws of zebrafishbehavioral responses under sudden exposure to several typical pollutants. It alsocombined with the presence of similar instruments in use false alarm rate and poorstability studies to provide reference and basis for better application of water qualitywarning systems based on changes of fish behavior.The behavioral effects of heavy metals and pestieide on zebrafish were detenninedby toxicity tests. Swimming changes in zebrafish were detected at a concentration aslow as1~10%of the LC50-24hwithin five hours (1TU, Toxic Unit). The behavioralresponses were time dependent: the first response might be avoidance (increased speedand turning frequency), followed by a second response of changed distribution(increased or decreased swimming depth) in the test tank.With the different concentrations of pollution exposure, changes in zebrafishbehavior were divided into three cases:(1)0.01TU, no significant behavioralregulation;(2)0.01~1TU, significant increase in swimming speed and turningfrequency (hyperactivity) occurred in a short response time during the first phase behavioral responses, but after a period of maintenance, there was a sudden decrease toequal or lower than unexposed conditions in both exposure tests;(3)2TU exposed,direct decrease in the strength of behavior. In addition, except in contaminants withobvious color and odor (such as Cr6+and dimethoate), the mean duration ofhyperactivity (T1), the time of swimming depth starting to change (T2) and exposureconcentration were significantly correlated. By comparing the duration of hyperactivityand the time until detection of surfacing, it could be identified that the time gap betweenthem decreased with the increased concentrations. Logarithmic curve fitting predictionmodel was established in the actual monitoring of water quality, both T1and T2valueswere able to be calculated as a preliminary determination on behalf of the extent ofwater contamination.Changes in behavior is not only a reaction of fish by the internal regulatorymechanisms to environmental stress, but also a result of its role in the environment.Acetylcholinesterase (AChE) decreased with decreasing speed in deltamethrin-exposure(p <0.01, r2=0.7103), but not in cadmium-exposure (p>0.05, r2=0.0646), which maycontribute to the duration difference. With the continuous exposure, speed and turningfrequency under both exposures decreased, even lower than the control group, whichindicated a possible energy reallocation from locomotion to detoxification processes(Consistently, the increased level of Catalase (CAT) and GSH were found).Normal zebrafish to light stimuli has obvious panic reaction to light stimuli, but bythe toxic effects of in pollutants affect with damages of nerve or tissue damage, thestartle response of zebrafish startle response to light stimuli was significantly weakened.This feature Use of light stimulation of could be used to check the facticity ofbehavioral reaction this feature, the Iuse of light in this study is the first non-invasivephysical stimulation genuine reaction toxicity testing behavioral responses, it is wasrecommended to that after stimulated in2min with light intensity500lx in2minstimulate long time, if the mean difference in speed was low at10mm/s, transfer timeslower than the mean difference as a validation of toxicity3n./10s, the true conditionwould be genuinely toxic.In summary, the monitored individual behaviors (swimming speed, turningfrequency and swimming depth) and fish school behaviors (average distance, dispersion and fractal dimension) can be effective indicators in zebrafish behaviorresponses. It was concluded that this on-line monitoring system could real-time monitorthe fish behavior changes, achieve monitor and early warn the sudden pollutionaccidents and could infer the time when the pollution outbreaks and the relative effectsconcentrations of the pollution. The behavioral responses under lethal concentrations ofdifferent chemicals and the mechanism of toxic effect were also discussed to someextent in this study, providing basis for the reliability and feasibility of early warning ofsudden pollution by the behavioral response of the fish. Compared with the traditionalindividual fish and single endpoints monitoring system, this vision-based real-timemonitoring on the behavior of zebrafish school provided more comprehensive andeffective information, which could be available to monitor the accidental pollution.