The physiological characteristics of zebra fish (Danio rerio) based on metabolism and behavior: A new method for the online assessment of cadmium stress.

In order to illustrate heavy metal ecotoxicology associated with interactions between chemicals and biological systems, we investigated physiological changes (metabolism and behavior response) of zebra fish (Danio rerio) under 48 h Cadmium chloride (CdCl2) exposure using online monitoring technique. The concentrations of CdCl2 were designed as 4.26, 42.6 and 85.2 mg/L, which were 0.1, 1.0, and 2.0 based on toxic unit (TU), respectively. The metabolism was assessed using the oxygen consumption (OC), and the behavior response was analyzed in behavior strength (BS). Significant inhibition of both OC and BS could be observed: OC was 617.39 ± 30.48 mg/kg/h in the control, and it decreased rapidly to 229.07 ± 28.66 mg/kg/h in 2.0 TU treatment. BS changed from 0.76 ± 0.07 (control) to 0.39 ± 0.04 (2.0 TU) with the increase of exposure concentrations. Further results suggested that both factors were related to diurnal variation during 48 h exposure, which could be regarded as circadian rhythms: the average values of OC and BS during photo-phase were significantly higher than both during scoto-phase in CdCl2 treatments (p < 0.05). After integrated analysis, the original values of both OC and BS with wide fluctuation showed a negative linear relationship with CdCl2 concentration. The levels of both OC and BS were positively correlated with CdCl2 (r = 0.93 and p < 0.01). It is suggested that both OC and BS provide an objective ground for CdCl2 stress assessment, and that also could be applied to test the changes of organisms quantitatively in toxic physiology.

Does time difference of the acetylcholinesterase (AChE) inhibition in different tissues exist? A case study of zebra fish (Danio rerio) exposed to cadmium chloride and deltamethrin.

In order to illustrate time difference in toxic effects of cadmium chloride (CdCl2) and deltamethrin (DM), AChE activities were measured in different tissues, liver, muscle, brain, and gill, of Zebra fish (Danio rerio) across different concentrations in this research. The average AChE activity decreased comparing to 0.0 TU with DM (82.81% in 0.1 TU, 56.14% in 1.0 TU and 44.68% in 2.0 TU) and with CdCl2 (74.68% in 0.1 TU, 52.05% in 1.0 TU and 50.14% in 2.0 TU) showed an overall decrease with the increase of exposure concentrations. According to Self-Organizing Map (SOM), the AChE activities were characterized in relation with experimental conditions, showing an inverse relationship with exposure time. As the exposure time was longer, the AChE activities were correspondingly lower. The AChE inhibition showed time delay in sublethal treatments (0.1 TU) in different tissues: the AChE was first inhibited in brain by chemicals followed by gill, muscle and liver (brain > gill > muscle > liver). The AChE activity was almost inhibited synchronously in higher environmental stress (1.0 TU and 2.0 TU). As the AChE inhibition can induce abnormal of behavior movement, these results will be helpful to the mechanism of stepwise behavior responses according to the time difference in different tissues rather than the whole body AChE activity.

Behavior persistence in defining threshold switch in stepwise response of aquatic organisms exposed to toxic chemicals.

As a characteristic in bacterial colony, persistence model described the dynamics of two subpopulations (normal (n) and persister (p)). In order to illustrate the switch of "Threshold" in the stepwise behavior responses of organisms, it is hypothesized that total behavior (Bt) of organisms consists of two types in behavior tendency, intoxication (Bp) and normal/recovery behavior (Bn). Both Bp and Bn could be concurrently affected by environmental stress E, and behavior response modes (M) are decided by the relationship between E and toxicity threshold of test organisms (Ti). The results suggested stress constant λ was decided by the constant rates gnE,gpE, an and ap. Due to different stress constant λ, the behavior responses of indicators showed great difference in different M, which included 'safe mode' (Ms), 'acclimation mode' (Mac), 'adjustment mode' (Maj) and 'toxic effect' (Mte). Usually, Bt during Ms could maintain around 0.8, and Mte would happen once it is lower than 0.2. According to the relationship between Bt values and E changes in 7 Majs, behavior persistence relying on adjustment could reflect the behavior homeostasis of organisms under environmental stress and be regarded as a threshold switch for the stepwise behavior responses. The mathematical analysis of behavior persistence allows making a quantitative prediction on environment assessment that would promote the emergence of persistence, as well as evaluating its ecological implications.