Impact of microplastics on the gut microbiota and digestive physiology of a freshwater fish species (e.g., Danio rerio) under varying exposure concentrations.

Project Abstract

Microplastics (MPs) pose a multifaceted threat to aquatic organisms, potentially altering gut microbiota composition, digestive enzyme activity, and overall physiological performance. This study investigates the effects of varying MP exposure concentrations on the gut microbial communities and digestive physiology of Danio rerio (zebrafish) over a 12-week exposure period, using environmentally relevant MPs with polymodal sizes (<5 mm, predominantly 1–100 ?m) and polystyrene as the model polymer. A factorial design was employed with three MP concentrations (low 0.1 mg/L, medium 1 mg/L, high 10 mg/L) and a clean water control, each with triplicate tanks. Zebrafish were monitored for survival, growth, hepatosomatic index, and gonadosomatic index to assess systemic health, while gut samples were collected at 4, 8, and 12 weeks for microbiome sequencing (16S rRNA amplicon) and metagenomic pathway analysis to identify shifts in community structure and functional potential. Digestive physiology was evaluated through assays of key enzymes (amylase, protease, lipase), malabsorption indicators, and intestinal histopathology to detect mucosal integrity, lipid accumulation, and inflammatory cell infiltration. Hydrogen peroxide and lipid peroxidation biomarkers were measured to assess oxidative stress in hepatic and intestinal tissues. The study hypothesizes that MPs induce dose-dependent alterations in gut microbiota, characterized by decreased bacterial diversity and enrichment of opportunistic taxa, along with diminished digestive enzyme activities and histological signs of enteropathy, mediated by epithelial disruption and systemic oxidative stress. Data were analyzed using multi-omics integration to correlate microbial dysbiosis with functional pathway perturbations and digestive performance metrics. Principal coordinates analysis (PCoA) and Bray–Curtis dissimilarity quantified microbiome shifts, while linear mixed-effects models evaluated time-dependent effects and tank effects. Functional predictions via PICRUSt2 and shotgun metagenomics were integrated with enzyme activity profiles to identify disrupted carbohydrate and protein digestion pathways and altered bile acid metabolism. Expected outcomes include a clear dose-response relationship where higher MP exposure correlates with reduced growth rate, increased lipid peroxidation, compromised intestinal barrier function, and perturbed microbial communities, particularly reductions in short-chain fatty acid-producing taxa. We anticipate differential effects between particle sizes, with smaller fractions eliciting more pronounced microbiome and digestive disturbances due to greater surface area and potential for cellular uptake. The study will contribute to mechanistic understanding of how microplastics influence host-microbe interactions and digestive physiology in freshwater teleosts, informing risk assessment and mitigation strategies for MP pollution in freshwater ecosystems. Potential limitations include variability in MP shape and aging, host genetics, and environmental co-factors, which will be addressed through rigorous experimental controls and replication, in addition to validating key findings with complementary in vitro gut models. The integration of microbial and host physiological data aims to establish predictive biomarkers for MP exposure and thresholds beyond which vertebrate health may be compromised.

Project Overview

What This Project Is About

---

A simple study to understand how tiny plastic particles in water affect the gut of a small fish, like the zebrafish. It looks at how these plastics change gut bacteria and the way the fish digests food, when the fish are exposed to different levels of plastics.

---

---

The Problem It Addresses

---

Microplastics are widespread in water and can be eaten by fish. We don’t fully know how these plastics alter gut microbes or digestion, which could affect fish health and aquatic food webs. This project fills that knowledge gap in a clear, beginner-friendly way.

---

---

Objectives of the Project

---

1. Describe what microplastics are and how they can enter a fish’s gut.
2. Measure changes in gut bacteria populations after exposure.
3. Assess changes in digestive enzymes and nutrient absorption.
4. Compare effects across different plastic exposure levels.
5. Summarize potential risks to fish health and ecosystems.

---

---

What You Will Do Step by Step

---

1. Review basic literature on microplastics and fish digestion.
2. Design a simple experiment with several plastic concentration groups.
3. Expose fish to plastics for a defined period under supervision.
4. Collect gut samples and analyze bacterial communities with straightforward tests.
5. Test digestive enzyme activity and measure digestion efficiency.
6. Analyze data using basic comparisons between groups.
7. Interpret what changes mean for fish health.

---

---

Expected Outcome

Clear, easy-to-understand results showing whether microplastics alter gut microbes and digestion, with practical implications for fish health and water quality policies.