Does the previous exposure to copper alter the pattern of avoidance by zebrafish in a copper gradient scenario? Hypothesis of time-delayed avoidance due to pre-acclimation

Comparative Analysis of Hydrogel Adsorption/Desorption with and without Surfactants

In this particular study, a hydrogel known as SAP-1 was synthesized through the grafting of acrylic acid-co-acrylamide onto pullulan, resulting in the creation of Pul-g-Poly (acrylic acid-co-acrylamide). Additionally, a sponge hydrogel named SAP-2 was prepared by incorporating the surfactant sodium dodecyl benzene sulfonate (SDBS) into the hydrogel through free radical solution polymerization. To gain further insight into the composition and properties of the hydrogels, various techniques, such as Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (1H NMR), atomic absorption spectroscopy, and field emission scanning electron microscopy (FE-SEM), were employed. Conversely, the absorption kinetics and the equilibrium capacities of the prepared hydrogels were investigated and analyzed. The outcomes of the investigation indicated that each of the synthesized hydrogels exhibited considerable efficacy as adsorbents for cadmium (II), copper (II), and nickel (II) ions. In particular, SAP-2 gel displayed a remarkable cadmium (II) ion absorption ability, with a rate of 190.72 mg/g. Following closely, SAP-1 gel demonstrated the ability to absorb cadmium (II) ions at a rate of 146.9 mg/g and copper (II) ions at a rate of 154 mg/g. Notably, SAP-2 hydrogel demonstrated the ability to repeat the adsorption-desorption cycles three times for cadmium (II) ions, resulting in absorption capacities of 190.72 mg/g, 100.43 mg/g, and 19.64 mg/g for the first, second, and third cycles, respectively. Thus, based on the abovementioned results, it can be concluded that all the synthesized hydrogels possess promising potential as suitable candidates for the adsorption and desorption of cadmium (II), copper (II), and nickel (II) ions.

Pre-exposure to seawater or chloride salts influences the avoidance-selection behavior of zebrafish larvae in a conductivity gradient

The risk assessment of freshwater salinization is constructed around standard assays and using sodium chloride (NaCl), neglecting that the stressor is most likely a complex mixture of ions and the possibility of prior contact with it, triggering acclimation mechanisms in the freshwater biota. To date, as far as we are aware of, no information has been generated integrating both acclimation and avoidance behavior in the context of salinization, that may allow these risk assessments upgrading. Accordingly, 6-days-old Danio rerio larvae were selected to perform 12-h avoidance assays in a non-confined 6-compartment linear system to simulate conductivity gradients using seawater (SW) and the chloride salts MgCl2, KCl, and CaCl2. Salinity gradients were established from conductivities known to cause 50% egg mortality in a 96-h exposure (LC50,96h,embryo). The triggering of acclimation processes, which could influence organisms' avoidance-selection under the conductivity gradients, was also studied using larvae pre-exposed to lethal levels of each salt or SW. Median avoidance conductivities after a 12-h of exposure (AC50,12h), and the Population Immediate Decline (PID) were computed. All non-pre-exposed larvae were able to detect and flee from conductivities corresponding to the LC50,96h,embryo, selecting compartments with lower conductivities, except for KCl. The AC50,12h and LC50,96h overlapped for MgCl2 and CaCl2, though the former is considered as more sensitive as it was obtained in 12 h of exposure. The AC50,12h for SW was 1.83-fold lower than the LC50,96h, thus, reinforcing the higher sensitivity of the parameter ACx and its adequacy for risk assessment frameworks. The PID, at low conductivities, was solely explained by the avoidance behavior of non-pre-exposed larvae. Larvae pre-exposed to lethal levels of salt or SW were found to select higher conductivities, except for MgCl2. Results indicated that avoidance-selection assays are ecologically relevant and sensitive tools to be used in risk assessment processes. Stressor pre-exposure influenced organisms' avoidance-selection behavior under conductivity gradients, suggesting that under salinization events organisms may acclimate, remaining in altered habitats.

Identification of nicotine-seeking and avoiding larval zebrafish using a new three-choice behavioral assay

Introduction

Nicotine dependence is one of the main causes of preventable diseases in the United States. Nicotine-seeking and avoidance behavioral assays in larval zebrafish could be used for identifying potential new pharmacotherapeutics in an early phase of drug discovery and could facilitate the identification of genes and genomic variations associated with nicotine-seeking and avoidance behavior.

Methods

A new three-choice behavioral assay has been developed for the identification of nicotine-seeking and avoiding larval zebrafish. The three choices are represented by three compartments of a gradient maze. Video-recording and subsequent quantitative analysis of the swimming track was carried out using EthovisionXT (Noldus).

Results

Three behavioral phenotypes could be identified. Nicotine-seeking larval zebrafish occupied nicotine compartments for longer periods and entered the nicotine-containing compartments most frequently. Nicotine-avoiders spent most of the cumulative time in the water compartment or entered the water compartment most frequently. Non-seekers remained in the center compartment for most of the time. In the gradient maze, about 20-30% of larval zebrafish had a preference for low nicotine concentrations whereas nicotine avoidance was stronger at higher nicotine concentrations. Lower concentrations of nicotine (0.63 μM, 6.3 μM) resulted in higher percentages of nicotine seekers whereas high nicotine concentrations (63 μM, 630 µM) resulted in higher percentages of nicotine avoiders. Pre-treatment of larval zebrafish with nicotine slightly increased the percentage of nicotine avoiders at lower nicotine concentrations. Treatment with varenicline strongly increased the percentage of nicotine avoiders at lower nicotine concentrations.

Conclusion

The results show that larval zebrafish have individual preferences for nicotine that could change with drug treatment. The three-choice gradient maze assay for larval zebrafish provides a new testing paradigm for studying the molecular and cellular mechanisms of nicotine action and the discovery of potential new pharmacotherapeutics for the treatment of smoking cessation.

Experimental evidence of contamination driven shrimp population dynamics: Susceptibility of populations to spatial isolation

Contamination is likely to affect the composition of an ecological landscape, leading to the rupture of ecological connectivity among habitats (ecological fragmentation), which may impact on the distribution, persistence and abundance of populations. In the current study, different scenarios within a spatially heterogeneous landscape were simulated in the Heterogeneous Multi-Habitat Assay System (HeMHAS) to evaluate the potential effect that contamination (copper at 0.5 and 25 μg/L) might have on habitat selection by the estuarine shrimp Palaemon varians in combination with two other ecological factors: predator presence and food availability. As a result, P. varians detected and avoided copper; however, in the presence of the predation signal, shrimps shifted their response by moving to previously avoided regions, even if this resulted in a higher exposure to contamination. When encouraged to move towards environments with a high availability of food, a lower connectivity among the shrimp populations isolated by both contamination and predation risk simultaneously was evidenced, when compared to populations isolated only by the risk of predation. These results indicate that contamination might: (i) trigger avoidance in shrimps, (ii) prevent colonization of attractive foraging areas, (iii) enhance populations' isolation and (iv), make populations more susceptible to local extinction.

Act now before its too late: Copper exposure drives chemo-ecology of predator-prey dynamics of freshwater common spiny loach, Lepidocephalichthys thermalis (Valenciennes, 1846)

Due to the extensive use of copper (Cu) in various commercial products, its existence in aquatic bodies (freshwater and marine) is not unusual. Cu is well known for its effect on the olfactory physiology of fish. However, there are limited studies on the effect of Cu on important ecological functions in fish (predator-prey dynamics) that are primarily influenced by olfaction. In a series of experiments, we studied the effect of Cu exposure on the chemoreceptive behavior of the prey fish, Lepidocephalichthys thermalis. Prey fishes were exposed to an environmentally relevant concentration (5 μg/L) of Cu for 3 h and the anti-predator responses against native (Channa gachua) and alien predatory fish (tilapia) were quantified using an ethological assay. Cu exposed prey fishes did not recognize the native predator and had a lower survival rate than control (unexposed) fishes in predation trials. Cu exposed prey fishes have failed to learn associatively to detect a non-native predator resulting in higher mortality in prey population in direct encounters with tilapia. However, such a lack of predator recognition was found to be short-term and the treated prey fishes recovered anti-predator responses within 72 h. In addition, Cu inactivated the alarm cue which acts as a signal for the presence of predators and ensures associative learning and therefore it was considered to be an 'info-disruptor' in the present study. These outcomes together demonstrate that even at low concentration, Cu influences ecological decisions and survival against predators. Owing to the ubiquitous occurrence of Cu in water bodies, the present investigation will contribute to the knowledge of how environmental stressors alter the crucial ecological decisions of prey individuals in aquatic ecosystems. In addition, we suggest that freshwater reservoirs containing high levels of Cu could be unsuitable for the long-term survival of prey fishes and freshwater biodiversity.