A Study On The Behavioral Response Mechanism Of Zebrafish Under Environmental Stress Based On AChE Analysis Of Sputum And Brain

With the rapid development of industrial economy, the increasingly serious water pollution is becoming more and more serious and the issue has attracted an intensive concern of society. At present, heavy metals and pesticides are two major pollutants for huge areas of water pollution, cause of their extensive application in the industry and the agriculture. Cadmium is a heavy metal pollutant which toxicity rank only second to mercury and the toxic effects will impact on digestion, immunity and reproduction of aquatic organisms. Deltamethrin, a typical pyrethroid pesticides, can block the signal pathway. Zebrafish is a generic model organism which were widely used in ecotoxicological studies. Acetylcholinesterase(AChE) is a key enzymes in the nerve conduction process, and the AChE activity of aquatic organisms can be used as biological indicator of water pollution. The external behaviors of aquatic organisms will change in order to adapt to the environment stress, maybe there is some kind of response relations between AChE and external behaviors. The AChE was studied in paper in order to evaluate the ecological toxicology of pollutants of different levels to the biological individuals, and trying to make clear the internal mechanism which affected their external behaviors.Cadmium chloride and deltamethrin were selected as the pollutants, and zebrafish as the biological subjects. The effect on AChE of brain and gill is detected while the zebrafish is exposed to different pollutants of different concentrations, and correlation analysis on AChE and the strength of behavior was carried out, the results show that:1. In acute toxicity experiments, the cadmium chloride and deltamethrin for zebrafish LC50-48 h were respectively 42.6mg/L and 5.2?g/L. There are great differences between different pollutants toxicity to zebrafish, which may be caused by different toxicity mechanisms of two kinds of pollutants on zebrafish. Cadmium chloride was absorbed or feeded through the gills directly, and produce toxic effects on aquatic organisms. Deltamethrin has high toxicity to zebrafish, since it belongs to nerve poison, which effecting on the nervous system and causing nerve muscle spasm, movement disorders, resulting in paralysis and even death. The mortality of zebrafish were positively related to pollutant concentrations.2. AChE activity showed a downward trend in the time of 48 hours' exposure in the two kinds of pollutants, the degree of AChE inhibition in gill is not the same while the concentration ratio of two kinds of pollutants is different. With the increasing of pollutants concentrations, the AChE inhibition degree in gill is increased. When exposed to lower concentrations of 0.1TU, AChE activity in gill fluctuations is relatively larger and the inhibition rate is lower. In the case of 1TU and 2TU groups, AChE activity in gill were induced increasing in the time period of 0.5h-1h, and then decreased to a very low level. After that, there is a slight rebound, which may be associated with the adjustments for adapting to the changes of the external environment. AChE inhibition is both related to exposure time and dose of pollutants.3. There are something in common for 48 hours' exposure in the two pollutants that the AChE inhibition rate of brain AChE in 1TU and 2TU groups were both significantly higher than that of the 0.1TU group which concentration is lower. AChE activity was decreased with the extension of exposure time. Generally speaking, AChE activity both in brain and in gill were consistent with The Stepwise Stress Model.4. The correlation analysis of the intensity of behavior and AChE inhibition showed that they have strong correlation at the ratio of 10:0 for 0.1TU concentration in gill of zebrafish. At the ratio of 3:7 for 2TU the two parameters have certain correlation, but the intensity is not high. For the case of the ratio of 7:3, 3:7 and 0:10 for 0.1TU, AChE inhibition and behavior strength of zebrafish were all correlated. The two parameters are closely correlated at the ratio of 0:10 for 1TU. The changing trends of AChE activity of brain is closer to the behavior changes.There are few studies about AChE activity both in brain and in gill of zabrafish exposuring in two pollutants with different impact mechanisms, and the correlation analysis between AChE activity and external behavior is rarely reported. This paper can provide a theoretical basis for future studies about cholinergic system and external behavior of zebrafish. The analysis of the internal mechanism of aquatic organisms with several kinds of indicators will play an important role in judging not only the type but also the degree of pollution in the water contamination incidents. It can also make a contribution to online monitoring of water quality.