Shining a Light on the Dark Side of Pollution: Unravelling the Impact of Emerging Contaminants on the Phototactic Responses of Aquatic Animals

Behavioural bioassays for analysing the movement patterns and direct neurological responses to stimuli such as chemical contaminants, light illumination, and shifts in water temperature, is an emerging field in ecotoxicology. Recent studies have outlined both morphological and neurological shifts in aquatic organisms when exposed to neurotoxic pollution as well as shifts in environmental conditions in the form of light availability and the introduction of light pollution during nighttime hours. The presence of neurotoxic and neuro-modulating contaminants has been shown to have subsequent influences on behavioural patterns of aquatic animals in the forms of phototaxis, chemotaxis, and thermotaxis. Impacted behaviours resulting from exposure to both light and neurotoxic chemical pollution include food searching, predator avoidance, and mating or reproductive activities. 

Phototaxis is the direct behavioural response to the presence of light stimuli and is utilised for essential functions such as food searching and consumption. Such responses to light stimuli can be observed in aquatic invertebrates and fish through the tracking and monitoring of their movement patterns when exposed to a light stimulus. This is a complex behavioural endpoint that can offer valuable insights into not only the neurological function of organisms, but also any influences resulting from exposure to sublethal concentrations of neurotoxic contaminants. However, the full extent of neurological influences of these neurotoxic chemicals, such as pharmaceutical products remain unknown making this a novel field in ecotoxicology and highlights a need for further behavioural assays and studies.

This project aims to contribute to this emerging field of research through the development of an innovative, cutting-edge analysis system called the “Test Chamber System” and employing innovative bioinformatics techniques and methodologies to inform future studies investigating animal behaviour. The Test Chamber System was developed in two different forms - the Horizontal Test Chamber System and the Vertical Test Chamber System. The Test Chamber System was continually developed over the 2-year duration of the research project with various upgrades including the addition of the sheet optic light guide thermal management system and the optimisation of the light stimulus control interface system aimed at eliminating uncontrolled environmental variables from influencing the accuracy and reliability of behavioural data and subsequent findings. 

Through the development of both the Horizontal and Vertical Test Chamber analysis systems, we can conduct phototactic assays investigating animal movement at both a horizontal and vertical axis, respectively. These Test Chamber Systems also enable the activating of light stimuli to expose subjects to differing wavelengths of light including Cool White, Green, Blue, and Red to accurately monitor the behavioural shifts that occur when the testing arena is illuminated with light. The utilisation of the Horizontal Test Chamber System for three phases of phototactic testing including social comparative, wavelength preferential, and neurotoxic exposure testing using both individual and grouped Daphnia carinata subjects outlined a range of neurological shifts when exposed to light stimulus. The activity of unexposed subjects in a control group was compared to the activity of subjects exposed, for a total of 14 days, to the metallic pollutants of lead and zinc as well as the emerging pharmaceutical pollutants of carbamazepine and ibuprofen. At environmentally relevant concentrations, treatment groups underwent the exposure period and exhibited varying differences in both movement patterns and phototactic responses to different light stimuli.

With the completion of this project, the influences of pollutant exposure on both the movement patterns and phototactic behaviours and preferences, which were previously hidden, were uncovered. These insights generated valuable and reliable behavioural data and provided new insights into the influences of anthropogenic activity on aquatic life. Alongside these conclusions, the development and optimisation of both the Horizontal and Vertical Test Chamber Systems provide an exceptionally reliable and cheap technology that facilitates the monitoring and analysis of small aquatic organisms within small aquatic test chambers with the use of animal tracking algorithms to produce accurate behavioural data sets. The optimisation of both the PMMA bonding techniques and bioinformatic analysis workflow procedures provide an efficient and reliable method for both the production and manufacturing of custom-made well plates such as the well plates used for testing during this project as well as the high throughput of phototactic analyses using the Test Chamber System for use in future studies.