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A fishy tale: the impact of multiple stressors on host behaviour, physiology, and susceptibility to infectious disease
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This PhD thesis studied how multiple stressors — including microplastics, chemicals, and disease — combine to affect fish behavior, physiology, and vulnerability to infections in freshwater habitats. Freshwater fish face converging threats that are driving population declines faster than any other vertebrate group.
Aquatic habitats are facing increased anthropogenic stressors that are associated with multiple species demise. The loss of species is, sadly, part of a wider global crisis with current extinction levels estimated to be a thousand-fold higher than the background extinction rate. Freshwater habitats in particular are facing higher rates of degradation than any other habitat and within these, fish species are being lost faster than their terrestrial counterparts. Beyond the importance of fish as keystone species, they are an invaluable source of protein for humanity and stocks are facing a state of collapse. A key threat facing the fish industry, including wild stocks, is increased infectious disease burdens. A major reason we are witnessing a continued increase in losses to disease is because fish species are experiencing increased stressors that are compromising host welfare that in turn impacts disease susceptibility. This PhD project focussed on how fish welfare is impacted by different biotic and abiotic stressors, with an emphasis on host immunity and disease resistance. To accomplish this project, freshwater fish host-parasite models were utilised permitting long-term monitoring of infections in real time. Most stressors investigated negatively impacted fish disease resistance, with the first stressor investigated being mechanical disturbance associated with routine transportation practices. Beyond the increased susceptibility to disease seen in fish hosts exposed to stressors, this PhD also revealed that noise pollution significantly increases host mortality rates. However, in response to the ecological stressor, flow, no changes to fish immune gene expressions or pathogen burdens were seen. With regards to implementing simple measures for effective disease control, this project has revealed how the addition of structural enrichment to fish tanks significantly improved disease resistance while also reducing agnostic behaviour. The universal physiological cost of infection by significantly increasing host metabolic rates was also revealed. The final experimental study assessed how one of the most prevalent contaminants, microplastic, impacted host disease resistance, growth and mortality. Microplastic at variable concentrations significantly increased disease susceptibility and host mortality. Ultimately, this PhD project has furthered our understanding of how multiple emerging and widespread stressors are impacting fish host welfare through the lens of host-pathogen dynamics.
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This study examined how combined exposure to microplastics and organic chemical pollutants affects freshwater organisms through a multi-stress approach, focusing on gut microbiome changes as an indicator. Microplastic exposure in combination with other pollutants altered microbiome composition more than either stressor alone, with potential consequences for host fitness and disease resistance.
Hampered Survival Strategies and Altered Fish Behaviour Under the Threat of Fluoxetine, Microplastics, Mercury Toxicity, Thermal Discharge, and Pesticides
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This review examines how multiple aquatic stressors — mercury pollution, microplastics, fluoxetine, pesticides, and thermal discharge — impair fish behavior and survival, covering disrupted predator avoidance, foraging, reproduction, and neurological function across species.
Interactive Threats: Multi-stress Systems in Aquatic Environments
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Researchers examined how aquatic organisms face multiple simultaneous stressors — including plastic pollution, climate change, altered pH, and habitat loss — finding that the combined interactive effects of these threats are poorly understood yet critical to developing effective conservation and management strategies.
Microplastics Induced Dysfunctions in Physiology and Behavior of Fish: A Comprehensive Review.
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Researchers comprehensively review how microplastics disrupt fish physiology, documenting effects on growth, blood chemistry, reproduction, oxidative stress, immune function, and behavior — tracing mechanisms from gastrointestinal damage and endocrine disruption to neurotoxicity and transgenerational harm — to inform ecological risk assessment in aquatic and fisheries contexts.
Impact of Plastic Pollution on Freshwater Fish: Pathways, Biological Effects, and Implications
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This review synthesizes current evidence on plastic pollution impacts on freshwater fish, documenting physiological effects including oxidative stress, endocrine disruption, immune impairment, and reproductive damage following ingestion and trophic transfer. The findings emphasize the need for targeted research and mitigation strategies to protect freshwater biodiversity and the human populations that depend on inland fisheries.
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